probe: declare usleep

Author: mcpplibs

.github/workflows/probe.yml

@@ -153,6 +153,7 @@ jobs:
           cat > ulock.c <<'EOF'
           #include <stdio.h>
           #include <stdint.h>
+          #include <unistd.h>
           #include <pthread.h>
           extern int __ulock_wait(uint32_t operation, void *addr, uint64_t value, uint32_t timeout_us);
           extern int __ulock_wake(uint32_t operation, void *addr, uint64_t wake_value);