Fix warnings that were exposed when running with SK_DEBUG enable on an optimized release build.

gyp/common.gypi

Index: gyp/common.gypi
diff --git a/gyp/common.gypi b/gyp/common.gypi
index e0196cfd2af70c1d46d2fe8a10c4a92af0c63051..9ca2895d540316cf76e20ad96bd651785ac7e252 100644
--- a/gyp/common.gypi
+++ b/gyp/common.gypi
@@ -102,6 +102,16 @@
           'Release_Developer': {
             'inherit_from': ['Release'],
             'defines': [ 'SK_DEBUG=1' ],
+            'conditions': [
+              [ 'skia_clang_build == 0', {
+                # gcc has problems providing useful warnings of these types for
+                # optimized builds.
+                'cflags': [
+                  '-Wno-maybe-uninitialized',
+                  '-Wno-strict-overflow',
+                ],
+              }],
+            ],
           },
         },
       }],