Initial step toward supporting qualification conversions (C++ 4.4).

Changes:
  - Sema::IsQualificationConversion determines whether we have a qualification
    conversion.
  - Sema::CheckSingleAssignment constraints now follows the C++ rules in C++,
    performing an implicit conversion from the right-hand side to the type of
    the left-hand side rather than checking based on the C notion of 
    "compatibility". We now rely on the implicit-conversion code to
    determine whether the conversion can happen or
    not. Sema::TryCopyInitialization has an ugly reference-related
    hack to cope with the initialization of references, for now.
  - When building DeclRefExprs, strip away the reference type, since
    there are no expressions whose type is a reference. We'll need to
    do this throughout Sema.
  - Expr::isLvalue now permits functions to be lvalues in C++ (but not
  in C).



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@57935 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/SemaCXX/decl-expr-ambiguity.cpp b/test/SemaCXX/decl-expr-ambiguity.cpp
index b2c3ea7..5a76b93 100644
--- a/test/SemaCXX/decl-expr-ambiguity.cpp
+++ b/test/SemaCXX/decl-expr-ambiguity.cpp
@@ -38,6 +38,6 @@
 int g(C);
 
 void foo() {
-  fn(1); // expected-error {{incompatible integer to pointer conversion passing 'int', expected 'int (*)(class C)'}}
+  fn(1); // expected-error {{incompatible type passing 'int', expected 'int (*)(class C)'}}
   fn(g); // OK
 }