AOT & IR Cache Planning

This is a high level ticket, to track the work that needs to be done for a fairly complete aot/ir cache setup. Follow up from #47 #693

## Current state
- FEXLoader can capture IR to aot files via `--aotircapture`
- FEXLoader can load IR from aot files via `--aotirload`
- FEXLoader can pre-process an entire elf with `--aotirgenerate`
- IR loading is done per executable file (.so or otherwise)
- IR loading depends on mmap hooks to detect when binaries are loaded
- IR is loaded via mmap w/ index
- Used modules create a .path entry in ~/.fex-emu/aotir/
- Scripts/FEXUpdateAOTIRCache.sh reads .path files and generates .aotir files for the matching elfs/so files

### Multi threaded AOTIR generation
- There's a POC branch, needs multiple thread contexts and some other tweaks

### Streamable AOTIR generation
- Move the index to the end of the file
- Stream writes

### Precompiled binary caching (~ 2-4 weeks to reviewable code)
- Needs our jit to be relocation-aware
- Needs our codegen to be relocation-optimized
- Needs similar logic to mmap-based ir loading for the metadata
- Needs relocation information to be stored and parsed and applied
- Preferably on a per-block use basis, to avoid stutters in large files
- Should introduce a FEXAOTCompiler to compile IR caches to binary caches
- Should introduce a new cache loading mode, `--aotbin-load` or such that loads binary caches