[Clang] Fix JIT test on 32-bit systems

As reported by mgorny at https://reviews.llvm.org/D159115#4638037, the
unsigned long long cast fails on 32-bit systems at least with GCC.

It looks like a pointer provenance/aliasing issue rather than a bug in GCC.

Acked by Vassil Vassilev on the original revision.

(cherry picked from commit 3403686b)