Use stat() to Check that File Should be chmod()-ed

Rather than special-casing a check for `/dev/null`, this uses `stat()` to
avoid `chmod()`-ing any non-regular file. I believe this is the desirable
behavior. `UTIL_chmod()` is never called on directories at the moment, only
output files.

programs/fileio.c

@@ -509,7 +509,7 @@ static int FIO_remove(const char* path)
 #if defined(_WIN32) || defined(WIN32)
     /* windows doesn't allow remove read-only files,
      * so try to make it writable first */
-    UTIL_chmod(path, _S_IWRITE);
+    UTIL_chmod(path, NULL, _S_IWRITE);
 #endif
     return remove(path);
 }
@@ -619,7 +619,7 @@ FIO_openDstFile(FIO_prefs_t* const prefs,
                && strcmp (srcFileName, stdinmark)
                && strcmp(dstFileName, nulmark) ) {
             /* reduce rights on newly created dst file while compression is ongoing */
-            UTIL_chmod(dstFileName, 00600);
+            UTIL_chmod(dstFileName, NULL, 00600);
         }
         return f;
     }