[mlir] [llvm] [clang] [flang] [clang-tools-extra] [lld] [RISCV][LLD] Add RISCV zcmt optimise in linker relaxation (PR #68551)

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Xinlong-Wu wrote:

Considering that the LLVM instance of Phabricator has been replaced by a static archive, it is not workable to review on Phabricator anymore. So I reopened this pr and synchronized the latest changes.

https://github.com/llvm/llvm-project/pull/68551