[orc-rt] Actually test orc-rt/bit.h functions. (#177300)
The unit test was copied from a similar test in llvm, and was still
qualifying calls with 'llvm::'. This was unintended, but happened to
work because LLVM's bit.h is transitively included through LLVM's gtest
headers. Qualifying with 'orc_rt::' tests the intended functions.
Thanks to @jaredwy for spotting this!
