Move SimpleAtoms.h to ReaderWriter.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@173380 91177308-0d34-0410-b5e6-96231b3b80d8
[Driver] Run the pass manager.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@173381 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF] Add very basic support for IFUNC.

This currently just generates the plt and got entries with correct
relocations. The writer will not know what to do with the relocations. Or the
got and plt entries for that matter.