[SR-16122] Migrate to new pass manager for optimization pipeline

[swift-ci]

Previous ID	SR-16122
Radar	None
Original Reporter	maskray (JIRA User)
Type	Task

Additional Detail from JIRA

Votes	0
Component/s
Labels	Task
Assignee	None
Priority	Medium

md5: 5a496fae08f9850d5b30cf81e8be4ab9

Issue Description:

Using LLVM's legacy PM for optimization pipeline was deprecated in 13.0.0 Support for the legacy pass manager is being actively removed in LLVM 15.

LLVM's legacy PM for optimization pipeline may be completely removed in 16.0.0 (llvm::create*Pass, populateModulePassManager, etc). llvm-project `clang/lib/CodeGen/BackendUtil.cpp` can serve as an example using the new pass manager.

lib/IRGen/IRGen.cpp performLLVMOptimizations is the main one to port.

[aschwaighofer]

Done