Relativize include dir for windows build

When we use relativized include dir, /showIncludes shows relativized
path for the files in include dir.

This is an effort of removing absolute path from compiling output.

Bug: 439949
Change-Id: I056cd8bb08c10f01855ef3bdb56ea1bcce1b769b
Reviewed-on: https://chromium-review.googlesource.com/1075947
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562599}
1 file changed