Fail on errors when building fuzzers

Fails on errors when building fuzzers with `fuzz.py` (adds `Werror`).
Currently allows `declaration-after-statement`, `c++-compat` and
`deprecated` as they are abundant in code (some fixes to
`declaration-after-statement` are presented in this commit).

tests/fuzz/regression_driver.c

@@ -44,11 +44,12 @@ int main(int argc, char const **argv) {
     fprintf(stderr, "WARNING: No files passed to %s\n", argv[0]);
   for (i = 0; i < files->tableSize; ++i) {
     char const *fileName = files->fileNames[i];
-    DEBUGLOG(3, "Running %s", fileName);
     size_t const fileSize = UTIL_getFileSize(fileName);
     size_t readSize;
     FILE *file;
 
+    DEBUGLOG(3, "Running %s", fileName);
+
     /* Check that it is a regular file, and that the fileSize is valid.
      * If it is not a regular file, then it may have been deleted since we
      * constructed the list, so just skip it, but return an error exit code.