cgo: use -I instead of -iquote for source header directories (#2687)

The go command uses -I for package directories, which makes
directories available for "" and <> includes. We should do the same.

We no longer use ctx.build_file_path, since that directory might not
actually provide any build files, and its value changed in Bazel
3.7.0.

Fixes #2685
2 files changed