Dimitry Andric:  Silence some miscellaneous warnings.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@167493 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/cmath b/include/cmath
index a70bbf2..d3fbfe6 100644
--- a/include/cmath
+++ b/include/cmath
@@ -1202,7 +1202,9 @@
 // fma
 
 inline _LIBCPP_INLINE_VISIBILITY float fmaf(float __x, float __y, float __z) _NOEXCEPT {return (float)((double)__x*__y + __z);}
+#ifndef FP_FAST_FMAF
 #define FP_FAST_FMAF
+#endif
 
 using ::fma;