[llvm] [PseudoProbe] Make probe discriminator compatible with dwarf base discriminator (PR #94506)

[via llvm-commits]

https://github.com/WenleiHe commented:

Looks good. It would be good to test:

1) This change has zero impact on CSSPGO builds (both pass1 and pass2). 
2) Generally how many (%) of total dwarf discriminator can fit in the 3 bits.

https://github.com/llvm/llvm-project/pull/94506