Add windows support for bazel build

[skeptic-monkey]

Attempt to fix #472

linux/darwnin builds are not strictly equivalent to windows build. But it seem to already be that case without bazel, as we use pre-generated glog headers, that have hardcoded namespace for example.

Also, it doesn't support static linkage, but again, that seemed to already be hardcoded that way for windows when using pre-generated headers.

Windows support is far from perfect but it is at a least a step forward.

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[skeptic-monkey]

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[drigz]

Thank you!

I noticed that the pregenerated config.h hardcodes GOOGLE_NAMESPACE=google. Could you add a comment to the top of glog.bzl saying Known issue: the namespace parameter is not supported on Win32.?

[drigz]

This will leak config.h into the include path, which may break targets that depend on glog and contain #include "config.h". Can you apply the pattern from bazelbuild/bazel#4463 to calculate the path of src/windows/, and add "-I" + src_windows to windows_only_copts?

[drigz]

Are these necessary in defines? If so, are they all necessary or can some be in copts?

It looks to me like the public headers have an #ifndef GOOGLE_GLOG_DLL_DECL section that should make them unnecessary, but perhaps I'm missing something.

[drigz]

Hi @skeptic-monkey, will you have bandwidth to take a look at the review comments? If not, just let me know, as this is a valuable change as-is, so I'd be happy to merge it and take a look at the config.h issue myself.

[skeptic-monkey]

I'll be able to have a look this weekend. From what I've seen after checking quickly, It's not that straightforward.

Anyway. I'll check and if I don't see an easy solution I'll let you know

[drigz]

You were right, it wasn't straightforward :) But I managed to find a workaround, so I took the liberty of merging this and creating a PR for the cleanups.

Thanks for the contribution!

[shahms]

FWIW, this breaks clients that use features = ["layering_check"] because the public glog library no longer exports any headers directly.