Find PLT entries for x86, x86_64, and AArch64.

This adds a new method to ELFObjectFileBase that returns the symbols and addresses of PLT entries.

This design was suggested by pcc and eugenis in https://reviews.llvm.org/D49383.

Differential Revision: https://reviews.llvm.org/D50203

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@340610 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed