Makefiles: Name object response files with .rsp extension

This is more consistent with the Ninja generator, and is necessary
for the IAR linker to recognize the argument as a response file.

Fixes: #24165

Source/cmMakefileTargetGenerator.cxx

@@ -2249,6 +2249,7 @@ void cmMakefileTargetGenerator::CreateObjectLists(
       std::string responseFileName =
         (responseMode == Link) ? "objects" : "deviceObjects";
       responseFileName += std::to_string(i + 1);
+      responseFileName += ".rsp";
 
       // Create this response file.
       std::string objects_rsp = this->CreateResponseFile(