Honor MAKECOMMAND value saved in cache (#11026)

Use a separate variable to pass to the BUILD_COMMAND call
and then use set(CACHE) to transfer that to MAKECOMMAND.
That way, if MAKECOMMAND is in the cache already, it is
left untouched. Fixes regression introduced in commit
0b38bb4c with the fix for bug #2336.

Thanks to Evgeniy P for the patch.

Modules/CTest.cmake

@@ -228,8 +228,10 @@ IF(BUILD_TESTING)
   ENDIF(NOT BUILDNAME)
 
   # the build command
-  BUILD_COMMAND(MAKECOMMAND CONFIGURATION "\${CTEST_CONFIGURATION_TYPE}")
-  SET(MAKECOMMAND ${MAKECOMMAND} CACHE STRING "Command to build the project")
+  BUILD_COMMAND(MAKECOMMAND_DEFAULT_VALUE
+    CONFIGURATION "\${CTEST_CONFIGURATION_TYPE}")
+  SET(MAKECOMMAND ${MAKECOMMAND_DEFAULT_VALUE}
+    CACHE STRING "Command to build the project")
 
   # the default build configuration the ctest build handler will use
   # if there is no -C arg given to ctest: