Swift/Ninja: Add description to Swift object build steps

By default, Ninja displays the full build command for the object which
is very verbose. Warnings are often lost in the noise, and compile
errors take some searching to find. If a build step fails, Ninja will
still print out the full build command, so there's no loss of useful
information.

Fixes: #25853

Source/cmNinjaTargetGenerator.cxx

@@ -1992,6 +1992,11 @@ void cmNinjaTargetGenerator::WriteSwiftObjectBuildStatement(
   std::string const moduleFilepath =
     this->ConvertToNinjaPath(cmStrCat(moduleDirectory, '/', moduleFilename));
 
+  vars.emplace("description",
+               cmStrCat("Building Swift Module '", moduleName, "' with ",
+                        sources.size(),
+                        sources.size() == 1 ? " source" : " sources"));
+
   bool const isSingleOutput = [this, compileMode]() -> bool {
     bool isMultiThread = false;
     if (cmValue numThreadStr =

Tests/RunCMake/Swift/IncrementalSwift-second-stdout.txt

@@ -1,3 +1,3 @@
-.*Building Swift object A.swiftmodule CMakeFiles(/|\\)A.dir(/|\\)a.swift.o(bj)?
+.*Building Swift Module 'A' with 1 source
-.*Building Swift object B.swiftmodule CMakeFiles(/|\\)B.dir(/|\\)b.swift.o(bj)?
+.*Building Swift Module 'B' with 1 source
 FAILED: B.swiftmodule CMakeFiles(/|\\)B.dir(/|\\)b.swift.o(bj)?