llvm-exegesis uses JIT to compile synthetic code snippets.
Focus of this patch is to provide support necessary for llvm-exegesis to work on the riscv64 platform.
It also fixes the following LLVM-Unit OrcJIT tests on riscv64:
Some of the OrcJIT tests keep failing on riscv64, just with a different message - unimplemented relocation type X instead of unsupported processor type.
NB I don't have commit access to the LLVM repo, so someone should commit on my behalf.