[Name lookup] Match macro introduced names based on their base names.

Some lookups, such as the ones used for protocol conformance checking,
provide full names (with arguments). Drop everything down to simple names
so they we don't skip macro expansions when we might need them.

(cherry picked from commit 706b3e1)

Author: DougGregor

lib/AST/NameLookup.cpp

@@ -1601,11 +1601,12 @@ namespace {
       macro->getIntroducedNames(
           attr->getMacroRole(), attachedTo, introducedNames);
       for (auto name : introducedNames)
-        allIntroducedNames.insert(name);
+        allIntroducedNames.insert(name.getBaseName());
     }
 
     bool shouldExpandForName(DeclName name) const {
-      return introducesArbitraryNames || allIntroducedNames.contains(name);
+      return introducesArbitraryNames ||
+          allIntroducedNames.contains(name.getBaseName());
     }
   };
 }