[llvm] [Support][APint] Optimize fallback case in APInt::reverseBits (PR #189291)

[Nikita Popov via llvm-commits]

nikic wrote:

For example, if BitWidth = 24, then none of the switch cases will match, and it will fall through to the generic case. But that one uses U.pVal while it should be using U.VAL in that case.

https://github.com/llvm/llvm-project/pull/189291