more cancellation points: tcdrain, clock_nanosleep

src/termios/tcdrain.c

 #include <termios.h>
 #include <sys/ioctl.h>
+#include "libc.h"
 
 int tcdrain(int fd)
 {
-	return ioctl(fd, TCSBRK, 1);
+	int ret;
+	CANCELPT_BEGIN;
+	ret = ioctl(fd, TCSBRK, 1);
+	CANCELPT_END;
+	return ret;
 }

src/time/clock_nanosleep.c

 #define SYSCALL_RETURN_ERRNO
 #include <time.h>
 #include "syscall.h"
+#include "libc.h"
 
 int clock_nanosleep(clockid_t clk, int flags, const struct timespec *req, struct timespec *rem)
 {
-	return syscall4(__NR_clock_nanosleep, clk, flags, (long)req, (long)rem);
+	int ret;
+	CANCELPT_BEGIN;
+	ret = syscall4(__NR_clock_nanosleep, clk, flags, (long)req, (long)rem);
+	CANCELPT_END;
+	return ret;
 }