Reland "[clang][FileManager] fillRealPathName even if we aren't opening the file"

This reverts commit e2bb3121fd4ab5b01f9ec1d2e3e9877db9c6a54c.
+ fixed test for Windows

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@354291 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed