test: include headers for used funcs
These funcs use things like wait/write/read/strcmp but sometimes
don't include the right header for them.
* test/Makefile: Add -Wall to CFLAGS.
* test/clone.c: Include unistd.h.
* test/fork.c: Include sys/wait.h.
* test/sig.c: Include unistd.h.
* test/sigkill_rain.c: Include sys/wait.h.
* test/vfork.c: Include sys/wait.h.
* test/wait_must_be_interruptible.c: Include string.h
diff --git a/test/clone.c b/test/clone.c
index 5de302f..bdce8b1 100644
--- a/test/clone.c
+++ b/test/clone.c
@@ -4,6 +4,7 @@
#include <stdio.h>
#include <stdlib.h>
#include <sched.h>
+#include <unistd.h>
int child(void* arg)
{