[BOLT] Account for stubs with symbols in plt (#192716)
LLD and bfd do not generate functions symbols for stubs in PLT. However,
mold does and trips the object discovery to create two functions (BF
then PLTFunc). This can cause symbol to be resoved with BF with
incorrect ADRP immediate field in AArch64.
The issue is described in more detail here:
https://github.com/llvm/llvm-project/issues/192552
