unix: Clean up includes.

Remove unnecessary includes. Add includes that improve portability.

unix/main.c

@@ -1,8 +1,11 @@
 #include <stdint.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
 #include <stdarg.h>
+#include <sys/stat.h>
+#include <sys/types.h>
 
 #include "nlr.h"
 #include "misc.h"
@@ -391,8 +394,6 @@ int main(int argc, char **argv) {
     return 0;
 }
 
-#include <sys/stat.h>
-
 uint mp_import_stat(const char *path) {
     struct stat st;
     if (stat(path, &st) == 0) {