minor issue on src/bootstrap/bootstrap.py

in bootstrap.py: 1101

   def bootstrap_binary(self):
        # this ONLY works if the compiler toolchain is not set. not sure
        # where this happens but this fixed it for me
        """Return the path of the bootstrap binary

        >>> rb = RustBuild()
        >>> rb.build_dir = "build"
        >>> rb.bootstrap_binary() == os.path.join("build", "bootstrap",
        ... "debug", "bootstrap")
        True
        """
        # print(self.build)
        # for some reason this isnt correct on my machine
        return os.path.join(self.bootstrap_out(), "debug", "bootstrap")

the above function does not work correctly as it does not take into account self.build, in rare cases, the script will have the build process place it in self.boostrap_out(), self.build_dir,"debug","bootstrap".
as I am not familiar with your build process I got past it by inserting the self.build_dir in the final line.

I am willing to contribute a fix if someone can fill me in on how the script currently works.

Summary

Command used

./configure --build x86_64-pc-windows-gnu
x.py setup

Expected behaviour

bootstrap to download, extract and build

Actual behaviour

toolchain downloaded and built boostrap successfully but the call to the boostrap executable failed
because the 'process' placed the artifacts in a different directory

Bootstrap configuration (bootstrap.toml)

# Use different pre-set defaults than the global defaults.
#
# See `src/bootstrap/defaults` for more information.
# Note that this has no default value (x.py uses the defaults in `bootstrap.example.toml`).
profile = 'dist'

[llvm]

[gcc]

[build]

# Build triple for the pre-compiled snapshot compiler. If `rustc` is set, this must match its host
# triple (see `rustc --version --verbose`; cross-compiling the rust build system itself is NOT
# supported). If `rustc` is unset, this must be a platform with pre-compiled host tools
# (https://doc.rust-lang.org/nightly/rustc/platform-support.html). The current platform must be
# able to run binaries of this build triple.
#
# If `rustc` is present in path, this defaults to the host it was compiled for.
# Otherwise, `x.py` will try to infer it from the output of `uname`.
# If `uname` is not found in PATH, we assume this is `x86_64-pc-windows-msvc`.
# This may be changed in the future.
build = 'x86_64-pc-windows-gnu'

# Arguments passed to the `./configure` script, used during distcheck. You
# probably won't fill this in but rather it's filled in by the `./configure`
# script. Useful for debugging.
configure-args = ['--build', 'x86_64-pc-windows-gnu']

[install]

[rust]

[dist]

[target.x86_64-pc-windows-gnu]

Operating system

build environment was msys2 on windows x86_64

HEAD

on commit index 9faa75e1848..f53259e91ee 100644
ca2139d3262232d6b15471783f503ffe125531f6

Additional context

<log>

Start in src/bootstrap/bootstrap.py around line 1101, focusing on RustBuild.bootstrap_binary and the bootstrap_out/build_dir paths. Reproduce the failure with ./configure --build x86_64-pc-windows-gnu followed by x.py setup in the reported MSYS2 environment. Done means the bootstrap executable is located and launched successfully when the build artifacts use the reported directory layout.