Merge pull request #26111 from compnerd/complexity-is-key

AST: add a workaround for VS2017

Author: compnerd

include/swift/AST/SimpleRequest.h

@@ -113,7 +113,9 @@ namespace detail {
 
   /// Extract the first, nearest source location from a tuple.
   template<unsigned Index, typename ...Types,
-           typename = typename std::enable_if<Index < sizeof...(Types)>::type>
+           typename = typename std::enable_if<sizeof...(Types) - Index
+                                                  ? true
+                                                  : false>::type>
   SourceLoc extractNearestSourceLocTuple(const std::tuple<Types...> &value) {
     SourceLoc loc = maybeExtractNearestSourceLoc(std::get<Index>(value));
     if (loc.isValid())