Use early expansion for debug_optimize

https://chromiumcodereview.appspot.com/10828084 tried to do this but did it
only for release_optimize.

BUG=139118,70107

Review URL: https://chromiumcodereview.appspot.com/10873039

git-svn-id: http://src.chromium.org/svn/trunk/src/build@153060 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -2042,7 +2042,7 @@
               '_DEBUG',
             ],
             'cflags': [
-              '-O>(debug_optimize)',
+              '-O<(debug_optimize)',
               '-g',
             ],
             'conditions' : [