[PECOFF] Rename getFinalSectionName -> getOutputSectionName.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@195855 91177308-0d34-0410-b5e6-96231b3b80d8
[PECOFF] Implement /merge option.

/MERGE:foo=bar command line option merges section foo to section bar. If
section bar does not exist, foo is just renamed as bar.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@195856 91177308-0d34-0410-b5e6-96231b3b80d8