[llvm] [CodeGen] Preserve branch weights from PGO profile during instruction selection at -O0 (PR #161620)

[Grigory Pastukhov via llvm-commits]

grigorypas wrote:

I added the check recommended by @apolloww. 

I also had to add command line parameters to llc to populate PGOOptions (similar to how it is done for opt). Otherwise, it was hard to design test.  

https://github.com/llvm/llvm-project/pull/161620