Use cmath in math.hpp

include/util/math.hpp

@@ -1,9 +1,10 @@
 #pragma once
 #include "util/common.hpp"
-#ifndef _GLIBCXX_USE_C99_MATH
-	#define _GLIBCXX_USE_C99_MATH
-#endif
-#include <math.h>
+#include <cmath>
+
+
+// Use a few standard math functions without std::
+using std::isfinite;
 
 
 namespace rack {