[LoongArch] Support LoongArch-specific amswap[_db].{b/h} and amadd[_db].{b/h} instructions (#113255)
Two options for clang: -mlam-bh & -mno-lam-bh.
Enable or disable amswap[__db].{b/h} and amadd[__db].{b/h} instructions.
The default is -mno-lam-bh.
Only works on LoongArch64.