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/CodeGen/CGExprConstant.cpp b/lib/CodeGen/CGExprConstant.cpp
index 0b109f9..37c9c36 100644
--- a/lib/CodeGen/CGExprConstant.cpp
+++ b/lib/CodeGen/CGExprConstant.cpp
@@ -199,8 +199,8 @@
     // Copy initializer elements. Skip padding fields.
     unsigned EltNo = 0;  // Element no in ILE
     bool RewriteType = false;
-    for (RecordDecl::field_iterator Field = RD->field_begin(CGM.getContext()),
-                                 FieldEnd = RD->field_end(CGM.getContext());
+    for (RecordDecl::field_iterator Field = RD->field_begin(),
+                                 FieldEnd = RD->field_end();
          EltNo < ILE->getNumInits() && Field != FieldEnd; ++Field) {
       if (Field->isBitField()) {
         if (!Field->getIdentifier())
@@ -263,8 +263,8 @@
       // Make sure that it's really an empty and not a failure of
       // semantic analysis.
       RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
-      for (RecordDecl::field_iterator Field = RD->field_begin(CGM.getContext()),
-                                   FieldEnd = RD->field_end(CGM.getContext());
+      for (RecordDecl::field_iterator Field = RD->field_begin(),
+                                   FieldEnd = RD->field_end();
            Field != FieldEnd; ++Field)
         assert(Field->isUnnamedBitfield() && "Only unnamed bitfields allowed");
 #endif