bazel: Non WSL Bash required on Windows

[ThadHouse]

bazelisk build //... fails with the following output.

ERROR: C:/users/thadh/documents/github/thadhouse/allwpilib/wpiutil/BUILD.bazel:199:25: Action wpiutil/wpiutil/shared/split/libwpiutil.so failed: (Exit 127): bash.exe failed: error executing Action command (from target //wpiutil:shared/wpiutil-symbolsplit) C:\WINDOWS\system32\bash.exe -c ... (remaining 1 argument skipped)
external/local_systemcore/bin/objcopy.bat: line 1: @echo: command not found
external/local_systemcore/bin/objcopy.bat: line 2: externalbazelrio_systemcore_toolchain_windowsbookwormbinaarch64-bookworm-linux-gnu-objcopy.exe: command not found
ERROR: C:/users/thadh/documents/github/thadhouse/allwpilib/wpiutil/BUILD.bazel:442:28 PackageZip wpiutil/wpiutil_shared_zip-opt-arch-systemcore.zip failed: (Exit 127): bash.exe failed: error executing Action command (from target //wpiutil:shared/wpiutil-symbolsplit) C:\WINDOWS\system32\bash.exe -c ... (remaining 1 argument skipped)
INFO: Elapsed time: 732.208s, Critical Path: 180.76s
INFO: 19802 processes: 11679 internal, 7902 local, 221 worker.
ERROR: Build did NOT complete successfully

[ThadHouse]

It turns out that by default, Bazel uses hardcoded paths for bash.exe, and if not found it just searches PATH. On Windows, PATH does include a bash, but it's WSL bash. That bash cannot be used to run windows executables, as its actually in the WSL environment.

The way to solve this is to point BAZEL_SH to a windows bash instance. Git For Windows installs one, and is a decent choice by default to use.

[AustinSchuh]

From a debugging session:

• Bazel wants to find a bash which it can use to run basic commands.
• In this case, bazel found the one from wsl. Which went very poorly.
• Setting BAZEL_SH to the bash from git fixed it.

We need to automate this so nobody else has to go through it. Probably sandbox a bash, lots of options.