In 4c93fcd35b, the default use case has been changed to support setting
a custom handler, but it's written in a way to only support MCUX and
SYSTICK based platforms. For any other platform the build break because
of undefined TIMER_IRQ_HANDLER and TIMER_IRQ_NUM.
Fix the conditional so that the custom timer line is only entered if a
custom handler is defined. The test would probably stil not run on those
platforms until a custom case is defined pointing at the custom timer
interrput handler, but at least it won't break CI.
Also drop a closing endif comment as that clearly became misleading.
Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>
7ddefbf369