checker: improve pub struct check (fix #14446) (#14777)

vlib/sync/channels.c.v

@@ -31,7 +31,7 @@ enum Direction {
 	push
 }
 
-struct Channel {
+pub struct Channel {
 	ringbuf   &u8 // queue for buffered channels
 	statusbuf &u8 // flags to synchronize write/read in ringbuf
 	objsize   u32

vlib/sync/sync_darwin.c.v

@@ -54,7 +54,7 @@ MacOSX has no unnamed semaphores and no `timed_wait()` at all
    so we emulate the behaviour with other devices
 */
 [heap]
-struct Semaphore {
+pub struct Semaphore {
 	mtx  C.pthread_mutex_t
 	cond C.pthread_cond_t
 mut:

vlib/sync/sync_default.c.v

@@ -60,7 +60,7 @@ struct RwMutexAttr {
 }
 
 [heap]
-struct Semaphore {
+pub struct Semaphore {
 	sem C.sem_t
 }
 

vlib/sync/sync_windows.c.v

@@ -38,7 +38,7 @@ mut:
 }
 
 [heap]
-struct Semaphore {
+pub struct Semaphore {
 	mtx  C.SRWLOCK
 	cond C.CONDITION_VARIABLE
 mut:

vlib/sync/waitgroup.c.v

@@ -25,7 +25,7 @@ fn C.atomic_compare_exchange_weak_u32(voidptr, voidptr, u32) bool
 //
 // [init_with=new_waitgroup] // TODO: implement support for init_with struct attribute, and disallow WaitGroup{} from outside the sync.new_waitgroup() function.
 [heap]
-struct WaitGroup {
+pub struct WaitGroup {
 mut:
 	task_count u32       // current task count - reading/writing should be atomic
 	wait_count u32       // current wait count - reading/writing should be atomic