Some cmake build improvements (#376)

* Change some cmake output to DEBUG level
Make SDK build more consistent with other libraries (use an INTERFACE marker library for inclusion tests)
Add PICO_SDK_PRE_LIST_FILES, PICO_SDK_POST_LIST_FILES build vars

* fix typo

* remove leftover debugging message

src/common/pico_sync/sem.c

@@ -6,6 +6,7 @@
 
 #include "pico/sem.h"
 #include "pico/time.h"
+#include "sys/select.h"
 
 void sem_init(semaphore_t *sem, int16_t initial_permits, int16_t max_permits) {
     lock_init(&sem->core, next_striped_spin_lock_num());