[llvm-jitlink] Use MachOObjectFile::getArchTriple for triple identifi… (#161799)
…cation.
Replaces a call to ObjectFile::makeTriple (still used for ELF and COFF)
with a call to MachOObjectFile::getArchTriple. The latter knows how to
build correct triples for different MachO CPU subtypes, e.g. arm64 vs
arm64e, which is important for selecting the right slice from universal
archives.