Rename lld:*_error::_ -> lld:*_error::ErrorCode.

Summary: Rename lld:*_error::_ -> lld:*_error::ErrorCode.

Reviewers: shankarke

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1851

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@192138 91177308-0d34-0410-b5e6-96231b3b80d8