using floor and ceil from math lib for rounding and truncation

src/frontend/numparam/mystring.c

@@ -10,6 +10,7 @@
 #include <ctype.h>
 #include <string.h>
 #include <memory.h>
+#include <math.h>
 
 #include "config.h"
 #ifdef HAS_WINDOWS
@@ -1122,11 +1123,11 @@ ival (char *s, int *err)
   return z;
 }
 
-#ifndef _MATH_H
+#ifndef HAVE_LIBM
 
 long
 np_round (double x)
-/* using <math.h>, it would be simpler: floor(x+0.5) */
+/* using <math.h>, it would be simpler: floor(x+0.5), see below */
 {
   double u;
   long z;
@@ -1207,4 +1208,4 @@ intp (double x)			/* integral part */
     return ceil (x);
 }
 
-#endif /* _MATH_H */
+#endif