Annotate SK_COMPILE_ASSERT's typedef as permissibly unused, to fix GCC 4.8 build warning. Patch originally by dholbert.

R=bsalomon@google.com

Review URL: https://codereview.chromium.org/22285002

git-svn-id: http://skia.googlecode.com/svn/trunk/include@10575 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/core/SkPostConfig.h b/core/SkPostConfig.h
index 0227575..07c1217 100644
--- a/core/SkPostConfig.h
+++ b/core/SkPostConfig.h
@@ -63,6 +63,14 @@
     #endif
 #endif
 
+#if !defined(SK_ATTRIBUTE)
+    #if defined(__clang__) || defined(__GNUC__)
+        #define SK_ATTRIBUTE(attr) __attribute__((attr))
+    #else
+        #define SK_ATTRIBUTE(attr)
+    #endif
+#endif
+
 #if !defined(SK_SUPPORT_GPU)
     #define SK_SUPPORT_GPU 1
 #endif
@@ -354,6 +362,12 @@
 
 //////////////////////////////////////////////////////////////////////
 
+#if !defined(SK_UNUSED)
+    #define SK_UNUSED SK_ATTRIBUTE(unused)
+#endif
+
+//////////////////////////////////////////////////////////////////////
+
 #ifndef SK_PRINTF_LIKE
 #if defined(__clang__) || defined(__GNUC__)
 #define SK_PRINTF_LIKE(A, B) __attribute__((format(printf, (A), (B))))
diff --git a/core/SkTypes.h b/core/SkTypes.h
index 48a6de8..0393691 100644
--- a/core/SkTypes.h
+++ b/core/SkTypes.h
@@ -127,7 +127,7 @@
 };
 
 #define SK_COMPILE_ASSERT(expr, msg) \
-    typedef SkCompileAssert<(bool(expr))> msg[bool(expr) ? 1 : -1]
+    typedef SkCompileAssert<(bool(expr))> msg[bool(expr) ? 1 : -1] SK_UNUSED
 
 /*
  *  Usage:  SK_MACRO_CONCAT(a, b)   to construct the symbol ab