[DebugInfo] Check DIEnumerator bit width when comparing for equality

As mentioned in D106585, this causes non-determinism, which can also be
shown by this test case being flaky without this patch.

We were using the APSInt's bit width for hashing, but not for checking
for equality. APInt::isSameValue() does not check bit width.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D115054