[QoI] Don't skip over protocols when importing Swift 2 type aliases

Protocols have the implicit Self generic parameter, which was
preventing this type alias from getting created, so some renamed
imported protocols for Swift 3 weren't emitting the expected
diagnostics and fix-its.

rdar://problem/26304496

Author: bitjammer

lib/ClangImporter/ImportDecl.cpp

@@ -1276,7 +1276,7 @@ namespace {
 
       // FIXME: We cannot currently handle generic types.
       if (auto generic = dyn_cast<GenericTypeDecl>(typeDecl)) {
-        if (generic->getGenericSignature())
+        if (generic->getGenericSignature() && !isa<ProtocolDecl>(typeDecl))
           return nullptr;
       }
 

test/ClangModules/swift2_warnings.swift

@@ -91,3 +91,5 @@ class X : NSDocument {
     return url
   }
 }
+
+func makeCopy<T: NSCopying>(thing: T) {} // expected-error {{'NSCopying' has been renamed to 'Copying'}} {{18-27=Copying}}