make sigsuspend a cancellation point

src/signal/sigsuspend.c

@@ -1,7 +1,12 @@
 #include <signal.h>
 #include "syscall.h"
+#include "libc.h"
 
 int sigsuspend(const sigset_t *mask)
 {
-	return syscall2(__NR_rt_sigsuspend, (long)mask, SYSCALL_SIGSET_SIZE);
+	int ret;
+	CANCELPT_BEGIN;
+	ret = syscall2(__NR_rt_sigsuspend, (long)mask, SYSCALL_SIGSET_SIZE);
+	CANCELPT_END;
+	return ret;
 }