add LoongArch NCG support

compiler/CodeGen.Platform.h

compiler/GHC/Cmm/CLabel.hs

compiler/GHC/CmmToAsm.hs

compiler/GHC/CmmToAsm/Dwarf/Constants.hs

compiler/GHC/CmmToAsm/LA64.hs

compiler/GHC/CmmToAsm/LA64.md

compiler/GHC/CmmToAsm/LA64/CodeGen.hs

compiler/GHC/CmmToAsm/LA64/Cond.hs

compiler/GHC/CmmToAsm/LA64/Instr.hs

compiler/GHC/CmmToAsm/LA64/Ppr.hs

compiler/GHC/CmmToAsm/LA64/RegInfo.hs

compiler/GHC/CmmToAsm/LA64/Regs.hs

compiler/GHC/CmmToAsm/PIC.hs

compiler/GHC/CmmToAsm/Reg/Graph/TrivColorable.hs

compiler/GHC/CmmToAsm/Reg/Linear.hs

compiler/GHC/CmmToAsm/Reg/Linear/FreeRegs.hs

compiler/GHC/CmmToAsm/Reg/Linear/LA64.hs

compiler/GHC/CmmToAsm/Reg/Target.hs

compiler/GHC/Driver/Backend.hs

compiler/GHC/Driver/DynFlags.hs