Support linux remote exec from windows

[cerisier]

Currently at least fails with:

ERROR: D:/_bazel/external/rules_zig++zig+zig_0.15.2_x86_64-linux/BUILD.bazel:5:14: validate Zig SDK version for toolchain @@rules_zig++zig+zig_0.15.2_x86_64-linux//:zig_toolchain [for tool] failed: (Exit 1): bash.exe failed: error executing ZigVersionValidation command (from zig_toolchain rule target @@rules_zig++zig+zig_0.15.2_x86_64-linux//:zig_toolchain) C:\Program Files\Git\usr\bin\bash.exe -c actual_version="$($1 version)"

{"msg":"executable file `C:/Program Files/Git/usr/bin/bash.exe` not found in $PATH: No such file or directory","level":"error","time":"2026-02-04T17:21:41.559907Z"}

[aherrmann]

I don't have a Windows environment ready to test this right now. But, here's some context on what may be going on.
The validation action is defined here. It is part of the Zig toolchain rule which provides the Zig toolchain itself. It's possible that the host and exec platforms get intermingled in a problematic way here. It looks like the Bash path is derived from the Windows (host) environment, but the action then fails because it executes on the remote Linux (exec) environment. The validation action uses ctx.actions.run_shell, which may be part of the culprit here as it may just pick the shell path from $BAZEL_SH or $(which bash).

[cerisier]

Impressed by the speed of the deduction haha. Took us hours in https://github.com/cerisier/toolchains_llvm_bootstrapped on a similar issue (with tests being built for the wrong platform but ran on remote)