Add support for more LLVM targets
Motivation
LLVM supports far more targets than the native code generator (NGC) available in GHC [1].
If GHC could be extended to provide LLVM backend support for LLVM targets such as M68k, MIPS, PowerPC and SPARC, it would for a faster compiler on these targets since LLVM-IR is more efficient than intermediate C code.
If LLVM support was available for 32-bit PowerPC, for example, it could easily be used to work around #23969.
Proposal
Enable LLVM target support for M68k, MIPS, PowerPC and SPARC.
[1] https://github.com/llvm/llvm-project/tree/main/llvm/lib/Target