Tutorial: Improve Step 5

* Updated output message
* Use 'target_compile_definitions' for HAVE_LOG and HAVE_EXP

Previously, the change from using TutorialConfig.h to
target_compile_definitions happened without explanation as part of Step 8.

Help/guide/tutorial/MultiPackage/MathFunctions/mysqrt.cxx

@@ -18,8 +18,8 @@ double mysqrt(double x)
   // if we have both log and exp then use them
 #if defined(HAVE_LOG) && defined(HAVE_EXP)
   double result = exp(log(x) * 0.5);
-  std::cout << "Computing sqrt of " << x << " to be " << result << " using log"
-            << std::endl;
+  std::cout << "Computing sqrt of " << x << " to be " << result
+            << " using log and exp" << std::endl;
 #else
   // use the table to help find an initial value
   double result = x;