try_compile: Use <resultvar> in scratch directory

Tweak the name of the scratch directory created by try_compile to
include the name of the variable receiving the compile result. This
should make it easier to find the result of a particular try_compile
when using --debug-trycompile.

Source/cmCoreTryCompile.cxx

@@ -447,7 +447,8 @@ bool cmCoreTryCompile::TryCompileCode(Arguments& arguments,
   if (useUniqueBinaryDirectory) {
     this->BinaryDirectory =
       cmStrCat(this->Makefile->GetHomeOutputDirectory(),
-               "/CMakeFiles/CMakeScratch/TryCompile-XXXXXX");
+               "/CMakeFiles/CMakeScratch/TryCompile-",
+               *arguments.CompileResultVariable, "-XXXXXX");
     cmSystemTools::MakeTempDirectory(this->BinaryDirectory);
   } else {
     cmSystemTools::MakeDirectory(this->BinaryDirectory);