[llvm] [Mips] Derive module ABI flags from a function definition (PR #220672)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Wait, wat?
> 
> Why is Mips trying to compute module-level ABI information from target features on functions, rather than deciding this based on float-abi/target-abi module flags?

This sort of abuse is kind of widespread. We need to fully eliminate the global MCSubtargetInfo.

ARM is the worst offender in this, but at least it's mostly computing module level features from functions in a vote-like direction where there is a conservative default. 

https://github.com/llvm/llvm-project/pull/220672