Fix hash_integer_value

Fix hash_integer_value

Broken in D18938 because underlying_type only works for enums and not all stdlibs are sad when given a non-enum. Bots error out with 'only enumeration types have underlying types'.

There's probably a clever enable_if-ism that I can do with underlying_type and the actual integer value, but is_integral_or_enum also accepts implicit conversion so I need to ponder my life choices a bit before committing to template magic. A quick fix for now.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@265880 91177308-0d34-0410-b5e6-96231b3b80d8