Use static assert instead of _LP64 (thanks Eddie!)

mkfs.c

@@ -11,9 +11,7 @@
 #include "stat.h"
 #include "param.h"
 
-#ifndef _LP64
-#error "Integers are not 32 bits"
-#endif
+#define static_assert(a, b) do { switch (0) case 0: case (a): ; } while (0)
 
 int nblocks = 985;
 int nlog = LOGSIZE;
@@ -68,6 +66,9 @@ main(int argc, char *argv[])
   char buf[512];
   struct dinode din;
 
+
+  static_assert(sizeof(int) == 4, "Integers must be 4 bytes!");
+
   if(argc < 2){
     fprintf(stderr, "Usage: mkfs fs.img files...\n");
     exit(1);