Bug 1067404 - Do not expect a copysign function to be defined in <cmath> with clang-cl; r=upstream

clang-cl defines __cplusplus to 201103L, but it uses the runtime library
provided by MSVC, so the copysign function will not be available there.

Review URL: https://codereview.chromium.org/526813002

gfx/skia/trunk/include/core/SkFloatingPoint.h

@@ -31,7 +31,7 @@ static inline float sk_float_pow(float base, float exp) {
 
 static inline float sk_float_copysign(float x, float y) {
 // c++11 contains a 'float copysign(float, float)' function in <cmath>.
-#if __cplusplus >= 201103L || (defined(_MSC_VER) && _MSC_VER >= 1800)
+#if (!defined(_MSC_VER) && __cplusplus >= 201103L) || (defined(_MSC_VER) && _MSC_VER >= 1800)
     return copysign(x, y);
 
 // Posix has demanded 'float copysignf(float, float)' (from C99) since Issue 6.