AST/SILGen support for constant string literals

rdar://30545013

lib/IRGen/GenMeta.cpp

@@ -5526,6 +5526,8 @@ SpecialProtocol irgen::getSpecialProtocolID(ProtocolDecl *P) {
   case KnownProtocolKind::BridgedNSError:
   case KnownProtocolKind::BridgedStoredNSError:
   case KnownProtocolKind::ErrorCodeProtocol:
+  case KnownProtocolKind::ExpressibleByBuiltinConstStringLiteral:
+  case KnownProtocolKind::ExpressibleByBuiltinConstUTF16StringLiteral:
     return SpecialProtocol::None;
   }