MinGW toolchain produces binaries that cannot be run with ctx.actions.run() by default

### Description of the problem / feature request:

Bazel's default MinGW toolchain produces binaries that depend on `C:\msys64\mingw64\bin\libstdc++-6.dll` and thus cannot be run without `C:\msys64\mingw64\bin` in the PATH.

A consequence of this is that Bazel rules fail to execute `cc_binary` binaries with `ctx.actions.run` when run with `--compiler=mingw-gcc`. The rule author must pass `use_default_shell_env = True` just to support MinGW, in combination with the user adding `C:\msys64\mingw64\bin` to the PATH of the Bazel invocation (or via `--action_env`).

### Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

Create a workspace with the following 4 files.

WORKSPACE

```python
# empty
```

BUILD.bazel

```python
load("//:defs.bzl", "foo")

cc_binary(
name = "write_hello",
srcs = ["write_hello.cpp"],
)

foo(
name = "hello.txt",
)
```

defs.bzl

```python
def _foo_impl(ctx):
output = ctx.actions.declare_file(ctx.label.name)
ctx.actions.run(
executable = ctx.executable._write_hello,
arguments = [output.path],
outputs = [output],
)
return [DefaultInfo(files = depset([output]))]

foo = rule(
implementation = _foo_impl,
attrs = {
"_write_hello": attr.label(
default = Label("//:write_hello"),
executable = True,
cfg = "exec",
),
},
)
```

write_hello.cpp

```cpp
#include

int main(int argc, char** argv) {
std::ofstream file;
file.open(argv[1]);
file << "Hello\n";
file.close();
}
```

`bazel build //:hello.txt` works:

```
INFO: Invocation ID: 1c85648d-229d-49fb-8185-63c98426363b
INFO: Analyzed target //:hello.txt (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
Target //:hello.txt up-to-date:
bazel-bin/hello.txt
INFO: Elapsed time: 0.188s, Critical Path: 0.01s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
```

`bazel build --compiler=mingw-gcc //:hello.txt` fails:

```
INFO: Invocation ID: c9bb725a-4f99-40b0-900f-5e88eacc4915
INFO: Build options --compiler and --host_compiler have changed, discarding analysis cache.
INFO: Analyzed target //:hello.txt (0 packages loaded, 173 targets configured).
INFO: Found 1 target...
ERROR: /BUILD.bazel:8:4: Action hello.txt failed: (Exit -1073741515): write_hello.exe failed: error executing command bazel-out\x64_windows-opt-exec-2B5CBBC6\bin\write_hello.exe bazel-out/x64_windows-fastbuild/bin/hello.txt
Target //:hello.txt failed to build
Use --verbose_failures to see the command lines of failed build steps.
INFO: Elapsed time: 0.336s, Critical Path: 0.09s
INFO: 3 processes: 1 disk cache hit, 2 internal.
FAILED: Build did NOT complete successfully
```

Opening `bazel-out\x64_windows-opt-exec-2B5CBBC6\bin\write_hello.exe` in File Explorer reveals the problem:


Adding `use_default_shell_env = True` to the `ctx.actions.run` and running `bazel build --compiler=mingw-gcc --action_env="PATH=C:\msys64\mingw64\bin" //:hello.txt` works:

```
INFO: Invocation ID: 7399a19e-6046-494f-bafa-48f8abe0b7f4
INFO: Analyzed target //:hello.txt (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
Target //:hello.txt up-to-date:
bazel-bin/hello.txt
INFO: Elapsed time: 0.170s, Critical Path: 0.01s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
```

but rule authors do not know this until a user complains that their rules don't work on MinGW. Binaries produce by the MinGW toolchain should work by default without special adaptions by rules to support it.

### What operating system are you running Bazel on?

> Microsoft Windows 10 Pro Build 19043

### What's the output of `bazel info release`?

> release 5.0.0