Index: include/llvm/Support/MathExtras.h
===================================================================
--- include/llvm/Support/MathExtras.h
+++ include/llvm/Support/MathExtras.h
@@ -456,8 +456,12 @@
 /// Log2 - This function returns the log base 2 of the specified value
 inline double Log2(double Value) {
 #if defined(__ANDROID_API__) && __ANDROID_API__ < 18
+#if !defined(HAVE_LOG2) || HAVE_LOG2
   return (double)__builtin_log2l(Value);
 #else
+  return __builtin_log(Value) / __builtin_log(2.0);
+#endif
+#else
   return log2(Value);
 #endif
 }