include unistd.h for smallint

Signed-off-by: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

libc/signal/sigwait.c

@@ -21,6 +21,7 @@
 #include <errno.h>
 #include <signal.h>
 #include <string.h>
+#include <unistd.h>
 
 #if defined __UCLIBC_HAS_REALTIME__