perfsession: support relocatable ELF files
perfsession: support relocatable ELF files

This adds support for finding function symbols in relocatable ELF
files such as shared libraries.

aclements/goperf,aclements/go-perf,aclements/go-perf,aclements/goperf,aclements/goperf,aclements/goperf,aclements/go-perf,aclements/go-perf