[ELF] Implement minimal support for .eh_frame_hdr.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@193662 91177308-0d34-0410-b5e6-96231b3b80d8
Use StringRef::startswith_lower().

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@193712 91177308-0d34-0410-b5e6-96231b3b80d8
Revert "[PECOFF] Add atoms to the PassManager file"

This reverts commit r193479.

The atoms are already added to the file, so re-adding them caused the YAML
writer to write the same atoms twice. That made the YAML reader to fail with
"duplicate atom name" error.

This is not the only error we've got for RoundTripYAMLPass for PECOFF, so we
cannot enable the test yet. More fixes will come.

Differential Revision: http://llvm-reviews.chandlerc.com/D2069

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@193762 91177308-0d34-0410-b5e6-96231b3b80d8