Add a GYP_DEFINE to force generating /Z7 flags for Visual C++.

This is required for parallel compilation tools that are unable to
support /Zi.

BUG=none
TEST=manual


Review URL: https://chromiumcodereview.appspot.com/10416043

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@138549 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed