Switch test back from getRealFileSystem to createPhysicalFileSystem

The tests change the VFS's working directory, but, we don't want to
change the actual process's working-directory, or it can break other
tests (depending on run order).

Fixes: df9a14d

Author: jyknight

clang/unittests/Sema/SemaNoloadLookupTest.cpp

@@ -58,7 +58,7 @@ class NoloadLookupTest : public ::testing::Test {
     addFile(FileName, Contents);
 
     CreateInvocationOptions CIOpts;
-    CIOpts.VFS = llvm::vfs::getRealFileSystem();
+    CIOpts.VFS = llvm::vfs::createPhysicalFileSystem();
     IntrusiveRefCntPtr<DiagnosticsEngine> Diags =
         CompilerInstance::createDiagnostics(*CIOpts.VFS,
                                             new DiagnosticOptions());