[VFS] Fix status() of opened redirected file

Make RedirectedFileSystem::openFilForRead(path)->status() the same as
RedirectedFileSystem::status(path). Previously we would just get the
status of the underlying real file, which would not have the IsVFSMapped
bit set.

This fixes rebuilding a module that has an include that is relative to
the includer where we will lookup the real path of that file before we
lookup the VFS location.

rdar://problem/23640339

llvm-svn: 255312
diff --git a/clang/test/VFS/Inputs/public_header.h b/clang/test/VFS/Inputs/public_header.h
index 09d9969..cc7bcb5 100644
--- a/clang/test/VFS/Inputs/public_header.h
+++ b/clang/test/VFS/Inputs/public_header.h
@@ -1,2 +1,3 @@
 #import <SomeFramework/public_header2.h>
+#import "public_header3.h" // includer-relative
 void from_framework(void);