[fuzz] Add a DEBUGLOG(3) statement to print file

Enable it by building with this command:

```
./fuzz.py build all --debug 3
```

tests/fuzz/fuzz_helpers.h

@@ -14,6 +14,7 @@
 #ifndef FUZZ_HELPERS_H
 #define FUZZ_HELPERS_H
 
+#include "debug.h"
 #include "fuzz.h"
 #include "xxhash.h"
 #include "zstd.h"

tests/fuzz/regression_driver.c

@@ -36,6 +36,7 @@ int main(int argc, char const **argv) {
     fprintf(stderr, "WARNING: No files passed to %s\n", argv[0]);
   for (i = 0; i < numFiles; ++i) {
     char const *fileName = files[i];
+    DEBUGLOG(3, "Running %s", fileName);
     size_t const fileSize = UTIL_getFileSize(fileName);
     size_t readSize;
     FILE *file;