MIPS1 Load Delay Slot support in LLVM

[cr1901]

This is required for e.g. PS1 support. I don't know how difficult it is to add support for this, but I imagine this is due more to lack of interest than anything on the LLVM side.

Cross-reference: simias/psx-sdk-rs#1

[asiekierka]

impiaaa/llvm-project@f2ecffe

This patch requires testing according to the developer, but it's a start.

[sajattack]

https://github.com/ayrtonm/llvm-project/tree/mips1-load-delay-slots