Revert "Enable MSRecordLayout in the presence of external sources."

This reverts commit r201810.

It was failing these tests on my workstation:
    Clang :: CodeGen/override-layout.c
    Clang :: CodeGenCXX/override-layout.cpp
    Clang :: PCH/check-deserializations.cpp

llvm-svn: 201823

clang/lib/AST/RecordLayoutBuilder.cpp

@@ -2892,7 +2892,7 @@ ASTContext::getASTRecordLayout(const RecordDecl *D) const {
 
   const ASTRecordLayout *NewEntry = 0;
 
-  if (isMsLayout(D)) {
+  if (isMsLayout(D) && !D->getASTContext().getExternalSource()) {
     NewEntry = BuildMicrosoftASTRecordLayout(D);
   } else if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D)) {
     EmptySubobjectMap EmptySubobjects(*this, RD);