Fix clang warnings in core/jni.

There are a few bugs in here too (mostly people expecting + to
concatenate C strings) :(

Change-Id: I0a243c05c4ea8b56e84896f37814d0fbea4c39d5
diff --git a/core/jni/android/graphics/Bitmap.cpp b/core/jni/android/graphics/Bitmap.cpp
index 70cf9a8..9c455df 100755
--- a/core/jni/android/graphics/Bitmap.cpp
+++ b/core/jni/android/graphics/Bitmap.cpp
@@ -43,8 +43,11 @@
 
 static void FromColor_D32_Raw(void* dst, const SkColor src[], int width,
                           int, int) {
+    // Needed to thwart the unreachable code detection from clang.
+    static const bool sk_color_ne_zero = SK_COLOR_MATCHES_PMCOLOR_BYTE_ORDER;
+
     // SkColor's ordering may be different from SkPMColor
-    if (SK_COLOR_MATCHES_PMCOLOR_BYTE_ORDER) {
+    if (sk_color_ne_zero) {
         memcpy(dst, src, width * sizeof(SkColor));
         return;
     }