sys::Path::GetCurrentDirectory has been removed. Use sys::fs::current_path.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@184004 91177308-0d34-0410-b5e6-96231b3b80d8
Revert "sys::Path::GetCurrentDirectory has been removed. Use sys::fs::current_path."

This reverts commit r184004.

This test has some dependency on the behavior of the old function on windows. I
added it back to llvm for now.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@184010 91177308-0d34-0410-b5e6-96231b3b80d8