Fix buildbot failure after D112940

Change a type from `int64_t` to `long long` to make a buildbot happy.

https://lab.llvm.org/buildbot/#/builders/196/builds/7371

```
error: no matching function for call to 'getAsSignedInteger'
 if (getAsSignedInteger(ValStr, 0, Val))
```

Worked With My Compiler (TM)