De-ASTContext-ify DeclContext.

Remove ASTContext parameter from DeclContext's methods. This change cascaded down to other Decl's methods and changes to call sites started "escalating".
Timings using pre-tokenized "cocoa.h" showed only a ~1% increase in time run between and after this commit.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@74506 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaTemplateInstantiateExpr.cpp b/lib/Sema/SemaTemplateInstantiateExpr.cpp
index 65a35f9..e1702b5 100644
--- a/lib/Sema/SemaTemplateInstantiateExpr.cpp
+++ b/lib/Sema/SemaTemplateInstantiateExpr.cpp
@@ -525,8 +525,7 @@
   const IdentifierInfo &Name 
     = SemaRef.Context.Idents.get("__builtin_shufflevector");
   TranslationUnitDecl *TUDecl = SemaRef.Context.getTranslationUnitDecl();
-  DeclContext::lookup_result Lookup 
-    = TUDecl->lookup(SemaRef.Context, DeclarationName(&Name));
+  DeclContext::lookup_result Lookup = TUDecl->lookup(DeclarationName(&Name));
   assert(Lookup.first != Lookup.second && "No __builtin_shufflevector?");
   
   // Build a reference to the __builtin_shufflevector builtin