Index: lib/Analysis/ConstantFolding.cpp
===================================================================
--- lib/Analysis/ConstantFolding.cpp
+++ lib/Analysis/ConstantFolding.cpp
@@ -37,6 +37,18 @@
 #include <cerrno>
 #include <cmath>
 
+#if defined(__ANDROID_NDK__)
+#include <android/api-level.h>
+
+#if __ANDROID_API__ < 18
+// log2 is missing from API < 18
+double log2(double d) { return (double)__builtin_log2l(d); }
+#else
+#include <math.h>
+#endif
+
+#endif // defined(__ANDROID_NDK__)
+
 #ifdef HAVE_FENV_H
 #include <fenv.h>
 #endif