Check compiler architecture flags in one place

src/util/math.h

@@ -29,6 +29,8 @@
 #ifndef UTIL_MATH_H_
 #define UTIL_MATH_H_
 
+#include "arch.h"
+
 #include <math.h>
 
 #ifdef __cplusplus
@@ -59,7 +61,7 @@
 
 static really_inline
 double our_pow(double x, double y) {
-#if defined(__AVX__)
+#if defined(HAVE_AVX)
     /*
      * Clear the upper half of AVX registers before calling into the math lib.
      * On some versions of glibc this can save thousands of AVX-to-SSE