Bazel send host-formatted paths to test-setup and generate-xml scripts

Description of the bug:

When running tests on a linux remote executor from a Windows host, I see spawns like this:

external\bazel_tools\tools\test\test-setup.sh
./cc_test

and

external\bazel_tools\tools\test\generate-xml.sh
bazel-out/x64_windows-fastbuild/testlogs/cc_test/test.log
bazel-out/x64_windows-fastbuild/testlogs/cc_test/test.xml
0
1

Which of course results in {"msg":"executable file external\bazel_tools\tools\test\test-setup.sh not found in $PATH: No such file or directory","level":"error","time":"2025-12-19T19:26:33.011523Z"}

The underlying executable is built correctly.

/Users/dzbarsky/Downloads/cc_test: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.0.0, not stripped

Which category does this issue belong to?

No response

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

No response

Which operating system are you running Bazel on?

Windows

What is the output of bazel info release?

release 9.0.0rc2

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

No response

What's the output of git remote get-url origin; git rev-parse HEAD ?

If this is a regression, please try to identify the Bazel commit where the bug was introduced with bazelisk --bisect.

No response

Have you found anything relevant by searching the web?

No response

Any other information, logs, or outputs that you want to share?

cc @fmeum