start loongarch compile

fix: modify the code to pass compile

add: add code for tcg_out_op, tcg_can_emit_vec_op, tcg_target_op_def to support new tcg_op

fix: fix bugs related to epilogue and ret_addr

fix: fix bug in qemu_ld_slow_path, the return register is wrong

qemu/include/elf.h

@@ -174,6 +174,7 @@ typedef struct mips_elf_abiflags_v0 {
 
 #define EM_NANOMIPS     249     /* Wave Computing nanoMIPS */
 
+#define EM_LOONGARCH        258 /* LoongArch */
 /*
  * This is an interim value that we will use until the committee comes
  * up with a final number.