[lld] [RISCV][LLD] Zcmt RISC-V extension in lld (PR #183450)

[via llvm-commits]

LukeZhuang wrote:

Rebased and moved everything into Arch/RISCV.cpp using the MaskRay's new `initTargetSpecificSections` hook: https://github.com/llvm/llvm-project/pull/184292. There are no changes in any target-independent area now.

https://github.com/llvm/llvm-project/pull/183450