Add initial support for LoongArch Architecture.

compiler/CodeGen.Platform.h

compiler/GHC/CmmToAsm.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/Target.hs

compiler/GHC/Driver/Pipeline/Execute.hs

compiler/GHC/Platform.hs

compiler/GHC/Platform/LoongArch64.hs

compiler/GHC/Platform/Regs.hs

compiler/ghc.cabal.in

configure.ac

hadrian/src/Oracles/Flag.hs

libraries/base/System/Info.hs

libraries/ghc-boot/GHC/Platform/ArchOS.hs

llvm-targets

m4/fptools_set_haskell_platform_vars.m4

m4/ghc_convert_cpu.m4

m4/ghc_tables_next_to_code.m4

m4/ghc_unregisterised.m4