[PassManager] add ReaderWriter{Native,YAML} to the Driver.

Enable this for the following flavors

a) core
b) gnu
c) darwin

Its disabled for the flavor PECOFF. Convenient markers are added with FIXME
comments in the Driver that would be removed and code removed from each flavor.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@193585 91177308-0d34-0410-b5e6-96231b3b80d8
[test] Fix a test failure, this test is only applicable in debug mode

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@193586 91177308-0d34-0410-b5e6-96231b3b80d8
[FileToMutable] Garbage collect unused private member

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@193588 91177308-0d34-0410-b5e6-96231b3b80d8