[llvm] [Mips] Add MipsPat `add $gp, (select $cond, tglobaladdr, tglobaladdr)` to parse MipsISD::GPRel TargetGlobalAddress (PR #165531)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

It's not obvious to me what the problem being solved here is from the description. It sounds like an optimization, but when I try the test it's a selection failure. This isn't really a solution for that, you need to MipsISD::GPRel as a leaf 

https://github.com/llvm/llvm-project/pull/165531