Fix absolute file paths checking for Windows

[stevenlr]

This is a fix for #476 and uses bazel_skylib's is_absolute function. I looked for other places that would need a similar fix but found only one more, so I may have missed some.

[stevenlr]

Hello, I rebased these changes on main but //tests/runfiles:runfiles_test seems to fail randomly now. Although when running locally it also sometimes fail on main.

Anyway, is there any update on moving this forward? No rush though, I'm fine with maintaining a fork for now.

[fmeum]

@stevenlr Could you share the failure?

Edit: Nvm, it's in CI:

unknown file: error: SEH exception with code 0xc0000005 thrown in the test body.
Stack trace:

@meteorcloudy Do you know what could cause this? The stack trace is empty.

[meteorcloudy]

Looks like a flake, retry worked.

[hvadehra]

@stevenlr Could you share the failure?

Edit: Nvm, it's in CI:

unknown file: error: SEH exception with code 0xc0000005 thrown in the test body.
Stack trace:

@meteorcloudy Do you know what could cause this? The stack trace is empty.

We've had a few internal reports of MSAN failures in a few singlejar tests , @cushon suspects they began after #417. Possibly related?

[fmeum]

That would make sense. I read through the change again but couldn't identify the issue.

Could you share the MSAN findings? I'll try to set up MSAN builds myself.

[fmeum]

@hvadehra nvm: #494