Ninja,Swift: correct response file handling

The response file was being written but not used due to the wrong
variable being configured for Swift.  Swift does compile+link in a
single phase and does not use the `<OBJECTS>` placeholder.  Use the
`<SWIFT_SOURCES>` placeholder instead for the response file substitution
which serves the same purpose.

Modules/CMakeSwiftInformation.cmake

@@ -18,10 +18,12 @@ if(CMAKE_Swift_COMPILER_ID)
 endif()
 
 set(CMAKE_INCLUDE_FLAG_Swift "-I ")
+
 set(CMAKE_Swift_DEFINE_FLAG -D)
 set(CMAKE_Swift_COMPILE_OPTIONS_TARGET "-target ")
 set(CMAKE_Swift_COMPILER_ARG1 -frontend)
 set(CMAKE_Swift_FRAMEWORK_SEARCH_FLAG "-F ")
+set(CMAKE_Swift_RESPONSE_FILE_LINK_FLAG @)
 
 # NOTE(compnerd) use the short form for convenience and ease of search.  They
 # are treated equivalent to their long form names as well as custom Swift

Source/cmNinjaNormalTargetGenerator.cxx

@@ -321,7 +321,11 @@ void cmNinjaNormalTargetGenerator::WriteLinkRule(bool useResponseFile)
         rspcontent = "$in_newline";
       }
       rspcontent += " $LINK_PATH $LINK_LIBRARIES";
-      vars.Objects = responseFlag.c_str();
+      if (this->TargetLinkLanguage == "Swift") {
+        vars.SwiftSources = responseFlag.c_str();
+      } else {
+        vars.Objects = responseFlag.c_str();
+      }
       vars.LinkLibraries = "";
     }