Fix our semantic analysis of

  unqualified-id '('

in C++. The unqualified-id might not refer to any declaration in our
current scope, but declarations by that name might be found via
argument-dependent lookup. We now do so properly.

As part of this change, CXXDependentNameExpr, which was previously
designed to express the unqualified-id in the above constructor within
templates, has become UnresolvedFunctionNameExpr, which does
effectively the same thing but will work for both templates and
non-templates.

Additionally, we cope with all unqualified-ids, since ADL also applies
in cases like

  operator+(x, y)




git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@63733 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/SemaCXX/conversion-function.cpp b/test/SemaCXX/conversion-function.cpp
index 17e73bc..f9dd600 100644
--- a/test/SemaCXX/conversion-function.cpp
+++ b/test/SemaCXX/conversion-function.cpp
@@ -9,7 +9,7 @@
   }
 
   float g() {
-    return operator float(); // expected-error{{use of undeclared 'operator float'}}
+    return operator float(); // expected-error{{no matching function for call to 'operator float'}}
   }
 };