More #include cleaning

- Drop Expr.h,RecordLayout.h from ASTContext.h (for DeclBase.h and
   SourceLocation.h)
 - Move ASTContext constructor into implementation

llvm-svn: 54627

clang/Driver/SerializationTest.cpp

@@ -16,6 +16,7 @@
 
 #include "clang/AST/ASTConsumer.h"
 #include "clang/AST/CFG.h"
+#include "clang/AST/Decl.h"
 #include "clang.h"
 #include "ASTConsumers.h"
 #include "clang/AST/TranslationUnit.h"