Disable COMDAT folding and OptimizeReferences for debug WinRT

In some configs these are enabled by default, and they causes linker
warnings (which are treated as errors).

BUG=angleproject:1250

Change-Id: Ia8d28e313c91f1d63248aa5c68d29f9c69b8d596
Reviewed-on: https://chromium-review.googlesource.com/317566
Tryjob-Request: Austin Kinross <aukinros@microsoft.com>
Tested-by: Austin Kinross <aukinros@microsoft.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
diff --git a/build/common.gypi b/build/common.gypi
index 17f8c22..7f58f82 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -176,7 +176,9 @@
                                 'AdditionalDependencies':
                                 [
                                     'dxgi.lib',
-                                ]
+                                ],
+                                'EnableCOMDATFolding': '1', # disable
+                                'OptimizeReferences': '1', # disable
                             }],
                         ],
                     },