Update compilation flags for all available compilers

Signed-off-by: Rafael Ravedutti <rafaelravedutti@gmail.com>

src/util.c

@@ -20,6 +20,8 @@
  *   with MD-Bench.  If not, see <https://www.gnu.org/licenses/>.
  * =======================================================================================
  */
+#include <string.h>
+
 #include <util.h>
 
 /* Park/Miller RNG w/out MASKING, so as to be like f90s version */