Start making all .cpp files compile-able on all platforms.

src/gpu/gl/mac/SkCreatePlatformGLContext_mac.cpp

Index: src/gpu/gl/mac/SkCreatePlatformGLContext_mac.cpp
diff --git a/src/gpu/gl/mac/SkCreatePlatformGLContext_mac.cpp b/src/gpu/gl/mac/SkCreatePlatformGLContext_mac.cpp
index fa4126a62c2312800c683929f5bcb38f87746e52..41585c8632ece4da3b1cfc5ccdcaa0e69853d93c 100644
--- a/src/gpu/gl/mac/SkCreatePlatformGLContext_mac.cpp
+++ b/src/gpu/gl/mac/SkCreatePlatformGLContext_mac.cpp
@@ -5,6 +5,9 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
+#include "SkTypes.h"
+#if defined(SK_BUILD_FOR_MAC)
+
 #include "gl/SkGLContext.h"
 #include "AvailabilityMacros.h"
 
@@ -117,3 +120,5 @@ SkGLContext* SkCreatePlatformGLContext(GrGLStandard forcedGpuAPI) {
     }
     return ctx;
 }
+
+#endif//defined(SK_BUILD_FOR_MAC)