Modules: Tolerate CMAKE_EXECUTE_PROCESS_COMMAND_ERROR_IS_FATAL

Capture `execute_process` calls' `RESULT_VARIABLE`.

We don't actually need to check the result as we presume the existing
logic is already adequate, and sometimes programs return non-zero values
as result of valid query.  I.e. this is a "safe" way to broadly protect
these scripts.

Issue: #27782