[ORC] add lazy jit support for riscv64

This adds resolver, indirection and trampoline stubs for riscv64,
allowing lazy compilation to work.

It assumes hard float extension exists. I don't know the proper way to detect it as Triple doesn't provide the interface to check riscv +f +d abi.

I am also not sure if orclazy tests should be enabled because lli needs an additional -codemodel=melany for tests to pass.

Reviewed By: lhames

Differential Revision: https://reviews.llvm.org/D122543