[llvm-branch-commits] [BOLT][NFC] Define getExprValue helper (PR #91663)

[Amir Ayupov via llvm-branch-commits]

https://github.com/aaupov created https://github.com/llvm/llvm-project/pull/91663

Move out common code extracting the address of a MCExpr. To be reused in
a follow-up diff.

Test Plan: NFC