In e838f27e0f3 the EndianTest.cpp unittest was updated to avoid using
`llvm::rotl` function, but the corresponding `orc_rt::rotl` function had
not been implemented yet.
This commit implements orc_rt::rotl, orc_rt::rotr, and
orc_rt::has_single_bit by copying their definitions from the
corresponding LLVM header (llvm-project/llvm/include/llvm/ADT/bit.h).
Unit tests for these functions are also copied from their LLVM
counterparts.
Thanks to @jaredwy for spotting this!
2b22d76ba7