[ORC-RT] Add bitmask-enum and bit_ceil utilities to the ORC runtime.

bitmask_enum.h is essentially a copy of llvm/ADT/BitmaskEnum.h, with some minor
cleanup and renaming.

The bit_ceil function is a placeholder for std::bit_ceil, which we can use once
compiler-rt can use c++20.

These utilities will be used to simplify bitfield enum usage in upcoming
ORC-RT patches.