build: Use compile_time_request system for init, tasks, and shutdown

Avoid using linker magic to define the init, task, and shutdown
functions.  Instead, use the compile_time_request system.  This
simplifies the build and produces more efficient code.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/generic/armcm_irq.c

@@ -40,7 +40,7 @@ irq_poll(void)
 }
 
 // Clear the active irq if a shutdown happened in an irq handler
-static void
+void
 clear_active_irq(void)
 {
     uint32_t psr;