Bug 1256552 - Disable C4577 to unblock compilation on VS2015; r=jrmuizel

As part of unblocking building with VS2015u1 in automation, I'm mass
disabling compiler warnings that are turned into errors. This is not
the preferred mechanism to fix compilation warnings. So hopefully
this patch never lands because someone insists of fixing the underlying
problem instead. But if it does land, hopefully the workaround is
only temporary.

MozReview-Commit-ID: BNhXxMhJaZh

--HG--
extra : rebase_source : 6d3746d99d0d058716a58f1ed1f0349e09866758
extra : source : cb49a303f86d6446bf1ed87d6e022e72a2ba25c7

gfx/thebes/moz.build

@@ -312,3 +312,7 @@ DEFINES['GRAPHITE2_STATIC'] = True
 if CONFIG['CLANG_CXX']:
     # Suppress warnings from Skia header files.
     SOURCES['gfxPlatform.cpp'].flags += ['-Wno-implicit-fallthrough']
+
+if CONFIG['_MSC_VER']:
+    # This is intended as a temporary hack to support building with VS2015.
+    CXXFLAGS += ['-wd4577']