Failing to build

Hello

I'm attempting to package a pypi project `policy_sentry` https://github.com/salesforce/policy_sentry

I've installed pyoxidizer into a docker container:
```dockerfile
ARG PYTHON_MAJOR_VERSION=3.7

# Download Terraform binary
FROM debian:buster-20191224-slim as pyoxidizer-base
ARG PYTHON_MAJOR_VERSION
RUN apt-get update
RUN apt-get install -y curl=7.64.0-4+deb10u1
RUN apt-get install -y unzip=6.0-23+deb10u1
RUN apt-get install -y zip=3.0-11+b1
RUN apt-get install -y python3=${PYTHON_MAJOR_VERSION}.3-1
RUN apt-get install -y python3-pip=18.1-5
RUN apt-get install -y python3-venv=3.7.3-1

RUN apt-get install -y build-essential=12.6
RUN apt-get install -y pkg-config=0.29-6
RUN apt-get install -y libssl-dev=1.1.1d-0+deb10u2

RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- --default-toolchain stable -y
RUN /root/.cargo/bin/cargo install pyoxidizer

WORKDIR /workspace
ADD policy_sentry .

CMD ["bash"]
```

My config file:
```
# This file defines how PyOxidizer application building and packaging is
# performed. See the pyoxidizer crate's documentation for extensive
# documentation on this file format.

# Obtain the default PythonDistribution for our build target. We link
# this distribution into our produced executable and extract the Python
# standard library from it.
def make_dist():
return default_python_distribution()

def make_macos_dist():
return PythonDistribution(
sha256="b46a861c05cb74b5b668d2ce44dcb65a449b9fef98ba5d9ec6ff6937829d5eec",
url="https://github.com/indygreg/python-build-standalone/releases/download/20190505/cpython-3.7.3-macos-20190506T0054.tar.zst"
)

def make_linux_dist():
return PythonDistribution(
sha256="608871543e6d2cb80e958638e31158355c578c114e12c77765ea5fb996a5a2c2",
local_path="/workspace/build/python_distributions/cpython-3.7.5-linux64-20191025T0506.tar.zst"
)

# Configuration files consist of functions which define build "targets."
# This function creates a Python executable and installs it in a destination
# directory.
def make_exe(dist):
# This variable defines the configuration of the
# embedded Python interpreter.
python_config = PythonInterpreterConfig(
# bytes_warning=0,
# dont_write_bytecode=True,
# ignore_environment=True,
# inspect=False,
# interactive=False,
# isolated=False,
# legacy_windows_fs_encoding=False,
# legacy_windows_stdio=False,
# no_site=True,
# no_user_site_directory=True,
# optimize_level=0,
# parser_debug=False,
# stdio_encoding=None,
# unbuffered_stdio=False,
# filesystem_importer=False,
# sys_frozen=False,
# sys_meipass=False,
# sys_paths=None,
# raw_allocator=None,
# terminfo_resolution="dynamic",
# terminfo_dirs=None,
# use_hash_seed=False,
# verbose=0,
# write_modules_directory_env=None,
# run_eval=None,
# run_module=None,
# run_noop=False,
# run_repl=True,
)

# The run_eval, run_module, run_noop, and run_repl arguments are mutually
# exclusive controls over what the interpreter should do once it initializes.
#
# run_eval -- Run the specified string value via `eval()`.
# run_module -- Import the specified module as __main__ and run it.
# run_noop -- Do nothing.
# run_repl -- Start a Python REPL.
#
# These arguments can be ignored if you are providing your own Rust code for
# starting the interpreter, as Rust code has full control over interpreter
# behavior.

# Produce a PythonExecutable from a Python distribution, embedded
# resources, and other options. The returned object represents the
# standalone executable that will be built.
exe = dist.to_python_executable(
name="policy_sentry",
config=python_config,
# Embed all extension modules, making this a fully-featured Python.
extension_module_filter='all',

# Only package the minimal set of extension modules needed to initialize
# a Python interpreter. Many common packages in Python's standard
# library won't work with this setting.
#extension_module_filter='minimal',

# Only package extension modules that don't require linking against
# non-Python libraries. e.g. will exclude support for OpenSSL, SQLite3,
# other features that require external libraries.
#extension_module_filter='no-libraries',

# Only package extension modules that don't link against GPL licensed
# libraries.
#extension_module_filter='no-gpl',

# Include Python module sources. This isn't strictly required and it does
# make binary sizes larger. But having the sources can be useful for
# activities such as debugging.
include_sources=True,

# Whether to include non-module resource data/files.
include_resources=False,

# Do not include functionality for testing Python itself.
include_test=False,
)

# Invoke `pip install` with our Python distribution to install a single package.
# `pip_install()` returns objects representing installed files.
# `add_python_resources()` adds these objects to our embedded context.
# exe.add_python_resources(dist.pip_install(["policy_sentry"]))

# Invoke `pip install` using a requirements file and add the collected files
# to our embedded context.
#exe.add_python_resources(dist.pip_install(["-r", "requirements.txt"]))

# Read Python files from a local directory and add them to our embedded
# context, taking just the resources belonging to the `foo` and `bar`
# Python packages.
#exe.add_python_resources(dist.read_package_root(
# path="/src/mypackage",
# packages=["foo", "bar"],
#)

# Discover Python files from a virtualenv and add them to our embedded
# context.
#exe.add_python_resources(dist.read_virtualenv(path="/path/to/venv"))

# Filter all resources collected so far through a filter of names
# in a file.
#exe.filter_from_files(files=["/path/to/filter-file"]))

# Return our `PythonExecutable` instance so it can be built and
# referenced by other consumers of this target.
return exe

def make_embedded_data(exe):
return exe.to_embedded_data()

def make_install(exe):
# Create an object that represents our installed application file layout.
files = FileManifest()

# Add the generated executable to our install layout in the root directory.
files.add_python_resource(".", exe)

return files

# Tell PyOxidizer about the build targets defined above.
register_target("dist", make_linux_dist)
register_target("exe", make_exe, depends=["dist"], default=True)
register_target("embedded", make_embedded_data, depends=["exe"], default_build_script=True)
register_target("install", make_install, depends=["exe"])

# Resolve whatever targets the invoker of this configuration file is requesting
# be resolved.
resolve_targets()

# END OF COMMON USER-ADJUSTED SETTINGS.
#
# Everything below this is typically managed by PyOxidizer and doesn't need
# to be updated by people.

PYOXIDIZER_VERSION = "0.6.0"
PYOXIDIZER_COMMIT = "UNKNOWN"
```

The build command fails with the line:
`register_target("dist", make_dist)`

```
root@ca4d128e7995:/workspace# /root/.cargo/bin/pyoxidizer build
resolving 1 targets
resolving target exe
resolving target dist
resolving Python distribution Url { url: "https://github.com/indygreg/python-build-standalone/releases/download/20191025/cpython-3.7.5-linux64-20191025T0506.tar.zst", sha256: "608871543e6d2cb80e958638e31158355c578c114e12c77765ea5fb996a5a2c2" }
Python distribution available at /workspace/./build/python_distributions/cpython-3.7.5-linux64-20191025T0506.tar.zst
reading data from Python distribution...
error: No such file or directory (os error 2)
```

I tried to build my own python standalone, and that succeeded with some tweaking, but fails to build for the same reason:

`register_target("dist", make_linux_dist)`
```
root@ca4d128e7995:/workspace# /root/.cargo/bin/pyoxidizer build
resolving 1 targets
resolving target exe
resolving target dist
resolving Python distribution Local { local_path: "/workspace/build/python_distributions/cpython-3.7.5-linux64-20191025T0506.tar.zst", sha256: "608871543e6d2cb80e958638e31158355c578c114e12c77765ea5fb996a5a2c2" }
existing /workspace/./build/python_distributions/cpython-3.7.5-linux64-20191025T0506.tar.zst passes SHA-256 integrity check
Python distribution available at /workspace/./build/python_distributions/cpython-3.7.5-linux64-20191025T0506.tar.zst
reading data from Python distribution...
error: No such file or directory (os error 2)
```

Attempting the macOS target fails also:
`register_target("dist", make_macos_dist)`

```
root@ca4d128e7995:/workspace# /root/.cargo/bin/pyoxidizer build
resolving 1 targets
resolving target exe
resolving target dist
resolving Python distribution Url { url: "https://github.com/indygreg/python-build-standalone/releases/download/20190505/cpython-3.7.3-macos-20190506T0054.tar.zst", sha256: "b46a861c05cb74b5b668d2ce44dcb65a449b9fef98ba5d9ec6ff6937829d5eec" }
Python distribution available at /workspace/./build/python_distributions/cpython-3.7.3-macos-20190506T0054.tar.zst
reading data from Python distribution...
error[PYOXIDIZER_BUILD]: Exec format error (os error 8)
--> ./pyoxidizer.bzl:75:11
|
75 | exe = dist.to_python_executable(
| ___________^
76 | | name="policy_sentry",
77 | | config=python_config,
78 | | # Embed all extension modules, making this a fully-featured Python.
... |
104 | | include_test=False,
105 | | )
| |_____^ to_python_executable()

error: Exec format error (os error 8)
```

And building a python-standalone dist for macOS also fails.

```
clang-macos> + cmake -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/tools/clang-macos -DCMAKE_C_COMPILER=/usr/bin/clang -DCMAKE_CXX_COMPILER=/usr/bin/clang++ -DCMAKE_ASM_COMPILER=/usr/bin/clang -DLLVM_ENABLE_LIBCXX=ON -DLLVM_OPTIMIZED_TABLEGEN=ON -DLLVM_TARGETS_TO_BUILD=X86 -DLLVM_LINK_LLVM_DYLIB=ON ../../llvm
clang-macos> /build/build-clang-macos.sh: line 56: /build/CMake.app/Contents/bin/cmake: cannot execute binary file
Traceback (most recent call last):
File "/Users/jslaman/git/policy_sentry_bin/python-build-standalone/cpython-unix/build.py", line 906, in
sys.exit(main())
File "/Users/jslaman/git/policy_sentry_bin/python-build-standalone/cpython-unix/build.py", line 755, in main
client, get_image(client, ROOT, BUILD, "clang"), platform=platform
File "/Users/jslaman/git/policy_sentry_bin/python-build-standalone/cpython-unix/build.py", line 215, in build_clang
build_env.run(build_sh, environment=env)
File "/Users/jslaman/git/policy_sentry_bin/python-build-standalone/pythonbuild/buildenv.py", line 64, in run
container_exec(self.container, program, user=user, environment=environment)
File "/Users/jslaman/git/policy_sentry_bin/python-build-standalone/pythonbuild/docker.py", line 128, in container_exec
raise Exception("exit code %d from %s" % (inspect_res["ExitCode"], command))
Exception: exit code 126 from /build/build-clang-macos.sh
make: *** [/Users/jslaman/git/policy_sentry_bin/python-build-standalone/build/clang-8.0.1-macos.tar] Error 1
```

Not sure what I'm doing wrong..

Reproduce the failure with the provided Docker setup and pyoxidizer.bzl, starting at the dist target and pyoxidizer.bzl line 75 where to_python_executable() is called. Compare the URL and local Python distribution cases, then verify the macOS case separately; done means identifying the cause of the missing-file and exec-format errors and making the build produce a clear, actionable result.

Written by the indexing model from the issue text.