Don't refresh stat() info for pcm files

Follow-up fix for 209138.  Actually, since we already have this file
open, we don't want to refresh the stat() info, since that might be
newer than what we have open (bad!).

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@209143 91177308-0d34-0410-b5e6-96231b3b80d8
test/CodeGenCXX/dllexport.cpp: -O2 and -disable-llvm-optzns aren't nedded

We only need them on the dllimport.cpp test to make sure that we emit code
for available_externaly functions, and don't inline the IR.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@209145 91177308-0d34-0410-b5e6-96231b3b80d8