Repeated "cmake . && ninja" calls were resulting in rebuilds every time.
Change the test so that it uses "file(WRITE" to generate a ".in" file and
then configure_file to "copy if different" that ".in" file to the final
generated source file.
Now, rebuilds will only occur if there are changes to the generated source
file on "cmake ." runs after the first one.
All supported memory checkers now write their output to a file. Use a dummy
checker that ignores the given filename and ensure that the missing file is
reported as error.