In commit 49948f7221 (ctest_memcheck: Add support for ThreadSanitizer,
2014-07-07, v3.1.0-rc1~322^2~1) and commit 1e005eadbc (CTest: Fix
MemoryCheckType from 'ctest -T MemCheck', 2014-07-15, v3.1.0-rc1~298^2),
the `CMakeCommand` internal setting was left set only when using `ctest
-S` scripts. Instead simply use CTest's corresponding CMake directly
without passing it through an internal setting.
Fixes: #20584
