[llvm] [Mips] Fix compiler crash when returning fp128 after calling a functi… (PR #117525)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm approved this pull request.

I'm still confused by this change, but it seems to be just following prior art in Mips that's been there since at least 2014. Whatever pre-processing it's doing should be consistently applied in all the calling convention contexts.

I don't understand why originalTypeIsF128 special cases a single element struct, and doesn't need to try to figure out the original element type from the EVT, or why this is how it implements that. But that's all pre-existing 

https://github.com/llvm/llvm-project/pull/117525