[lld] [lld][ELF][RISCV] Add Zcmt table-jump relaxation support (PR #206338)

[via llvm-commits]

nivanovi-mips wrote:

@jrtc27 @MaskRay @topperc Do you guys think there's any hope of some version of this optimization is likely to land any time soon? There appear to have been ~5 different attempts at implementing it (the 3 listed in the description, https://reviews.llvm.org/D134600 and this PR itself). TBH, we have been using (a slightly modified version of) the implementation at the Phabricator link for a couple of years now and find this to be useful for code size reduction. However, we'll gladly switch to whatever implementation the community settles on.

I will pull in this patch and run some tests on it in the hopes of helping unblock the PR, but I don't have the adequate depth of expertise with LLD + RISC-V to provide a final approval to get this merged in.

https://github.com/llvm/llvm-project/pull/206338