ELF: Improve error handling of unknown emulation names.
ELF: Improve error handling of unknown emulation names.

This patch reverts r253985 and implements the same feature
in a less intrusive way.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@254004 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld