Fix Clang build on Android.

The optimize attribute is not supported with Clang/ARM r161757.

This warning, turned into an error, is emitted by -Wattribute (implicitly set).
Review URL: https://codereview.appspot.com/6489045

git-svn-id: http://skia.googlecode.com/svn/trunk@5316 2bbb7eff-a529-9590-31e7-b0007b416f81

include/core/SkPreConfig.h

@@ -189,5 +189,32 @@
 #  define  SK_PURE_FUNC  /* nothing */
 #endif
 
+//////////////////////////////////////////////////////////////////////
+
+/**
+ * SK_HAS_ATTRIBUTE(<name>) should return true iff the compiler
+ * supports __attribute__((<name>)). Mostly important because
+ * Clang doesn't support all of GCC attributes.
+ */
+#if defined(__has_attribute)
+#   define SK_HAS_ATTRIBUTE(x) __has_attribute(x)
+#elif defined(__GNUC__)
+#   define SK_HAS_ATTRIBUTE(x) 1
+#else
+#   define SK_HAS_ATTRIBUTE(x) 0
 #endif
 
+/**
+ * SK_ATTRIBUTE_OPTIMIZE_O1 can be used as a function attribute
+ * to specify individual optimization level of -O1, if the compiler
+ * supports it.
+ *
+ * NOTE: Clang/ARM (r161757) does not support the 'optimize' attribute.
+ */
+#if SK_HAS_ATTRIBUTE(optimize)
+#   define SK_ATTRIBUTE_OPTIMIZE_O1 __attribute__((optimize("O1")))
+#else
+#   define SK_ATTRIBUTE_OPTIMIZE_O1 /* nothing */
+#endif
+
+#endif

src/opts/SkBitmapProcState_opts_arm.cpp

@@ -16,7 +16,7 @@ void SI8_D16_nofilter_DX_arm(
     const SkBitmapProcState& s,
     const uint32_t* SK_RESTRICT xy,
     int count,
-    uint16_t* SK_RESTRICT colors) __attribute__((optimize("O1")));
+    uint16_t* SK_RESTRICT colors) SK_ATTRIBUTE_OPTIMIZE_O1;
 
 void SI8_D16_nofilter_DX_arm(const SkBitmapProcState& s,
                              const uint32_t* SK_RESTRICT xy,
@@ -107,7 +107,7 @@ void SI8_opaque_D32_nofilter_DX_arm(
     const SkBitmapProcState& s,
     const uint32_t* SK_RESTRICT xy,
     int count,
-    SkPMColor* SK_RESTRICT colors) __attribute__((optimize("O1")));
+    SkPMColor* SK_RESTRICT colors) SK_ATTRIBUTE_OPTIMIZE_O1;
 
 void SI8_opaque_D32_nofilter_DX_arm(const SkBitmapProcState& s,
                                     const uint32_t* SK_RESTRICT xy,