[lld][LoongArch] GOT indirection to PC relative optimization (#123743) In LoongArch, we try GOT indirection to PC relative optimization in normal or medium code model, whether or not with R_LARCH_RELAX relocation. From: * pcalau12i $a0, %got_pc_hi20(sym_got) * ld.w/d $a0, $a0, %got_pc_lo12(sym_got) To: * pcalau12i $a0, %pc_hi20(sym) * addi.w/d $a0, $a0, %pc_lo12(sym) If the original code sequence can be relaxed into a single instruction `pcaddi`, this patch will not be taken (see https://github.com/llvm/llvm-project/pull/123566). The optimization related to GOT is split into two locations because the `relax()` function is part of an iteration fixed-point algorithm. We should minimize it to achieve better linker performance. Note: Althouth the optimization has been performed, the GOT entries still exists, similarly to AArch64. Eliminating the entries will increase code complexity.
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