Add float.h. It exists even if the environment was freestanding. It has been supported since C89.

src/numeric.c

@@ -9,6 +9,7 @@
 #include "mruby/string.h"
 #include "mruby/array.h"
 
+#include <float.h>
 #include <math.h>
 #include <assert.h>
 #include <stdlib.h>
@@ -17,10 +18,6 @@
 #include <floatingpoint.h>
 #endif
 
-#ifdef HAVE_FLOAT_H
-#include <float.h>
-#endif
-
 #ifdef HAVE_IEEEFP_H
 #include <ieeefp.h>
 #endif