Fix file name resolution in nested response files

Fix file name resolution in nested response files

If a response file in construct `@file` was specified by relative name,
constructs `@file` nested within it were resolved incorrectly if the
flag RelativeNames in call to ExpandResponseFile was set to true.
This feature is used in configuration files, tests for it are in
respective change (see D24933).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@287482 91177308-0d34-0410-b5e6-96231b3b80d8