[lld] [lld][ELF] Support relax R_LARCH_{ALIGN, PCALA_{HI20,LO12}, GOT_PC_{HI20,LO12}} (PR #78692)

[WÁNG Xuěruì via llvm-commits]

xen0n wrote:

Sorry for the late reply, but I agree with cherry-picking this change into LLVM 18, at least the `R_LARCH_ALIGN` bits. Because while linker relaxation is strictly a performance optimization and can safely be omitted without creating issues besides slower code, the unfortunate fact is that `R_LARCH_ALIGN` is already being used to implement alignment directives (so it's already popping out in the wild), and correctly handling of this reloc apparently requires implementing enough of relaxation mechanism.

https://github.com/llvm/llvm-project/pull/78692