Give every file that ASTReader loads a type: module, PCH, precompiled preamble or main file. Base Decls' PCHLevel on this to make it more sane.

llvm-svn: 115626
diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index 19d1690..7b87d3c 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -479,7 +479,7 @@
   Reader->setListener(new ASTInfoCollector(LangInfo, HeaderInfo, TargetTriple,
                                            Predefines, Counter));
 
-  switch (Reader->ReadAST(Filename)) {
+  switch (Reader->ReadAST(Filename, ASTReader::MainFile)) {
   case ASTReader::Success:
     break;
 
@@ -1305,10 +1305,7 @@
   if (!getOnlyLocalDecls())
     return Decl::MaxPCHLevel;
 
-  unsigned Result = 0;
-  if (isMainFileAST() || SavedMainFileBuffer)
-    ++Result;
-  return Result;
+  return 0;
 }
 
 ASTUnit *ASTUnit::LoadFromCompilerInvocation(CompilerInvocation *CI,