Remove all implicit definitions of compiler provided functions.

<strings.h> cause strncasecmp to be define.

src/asm/yaccprt1.y

@@ -1,10 +1,12 @@
 %{
+#define _XOPEN_SOURCE 500
 #include <ctype.h>
 #include <errno.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <strings.h>
 
 #include "asm/symbol.h"
 #include "asm/asm.h"