Use commit_id.py on Windows, and handle missing git.

This allows us to delete the Windows batch file.

Changes the commit_id script to take the working directory so that it
can be called from a different working directory than the angle
repository is in.

Renames the generated commit header to angle_commit.h. This is being
written to the shared generated code directory for the entire build,
and "commit.h" is insufficiently unique.

BUG=angle:669

Change-Id: I35e80411a7e8ba1e02ce3f6a4fc54ed4dbc918f3
Reviewed-on: https://chromium-review.googlesource.com/202048
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>
diff --git a/generate_projects b/generate_projects
index 6743254..8175277 100644
--- a/generate_projects
+++ b/generate_projects
@@ -34,6 +34,7 @@
     gyp_cmd += ' -D angle_build_tests=' + ('1' if build_tests else '0')
     gyp_cmd += ' -D angle_build_samples=' + ('1' if build_samples else '0')
     gyp_cmd += ' -D release_symbols=' + ('true' if release_symbols else 'false')
+    gyp_cmd += ' -D angle_use_commit_id=0'
     gyp_cmd += ' ' + os.path.join(script_dir, 'all.gyp')
 
     print 'Generating projects to ' + generation_dir + ' from gyp files...'