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/Makefile b/test/Makefile
index c6ce99c..781e1f6 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -1,3 +1,5 @@
+CFLAGS += -Wall
+
all: \
vfork fork sig skodic clone leaderkill childthread \
sigkill_rain wait_must_be_interruptible threaded_execve