When the COPY_FILE operation fails optionally capture the error message
with a COPY_FILE_ERROR option instead of reporting the error
immediately.  This gives callers a chance to do something else or report
the error.

Teach the RunCMake.try_compile test to cover bad argument combinations
involving COPY_FILE_ERROR.  Teach the TryCompile test to cover the case
of a COPY_FILE error message captured by COPY_FILE_ERROR.