u.h: add Solaris 5.10 to makecontext list
diff --git a/include/u.h b/include/u.h
index 2d29a36..56ed521 100644
--- a/include/u.h
+++ b/include/u.h
@@ -7,7 +7,7 @@
#define __BSD_VISIBLE 1 /* FreeBSD 5.x */
#if defined(__sun__)
# define __EXTENSIONS__ 1 /* SunOS */
-# if defined(__SunOS5_6__) || defined(__SunOS5_7__) || defined(__SunOS5_8__)
+# if defined(__SunOS5_6__) || defined(__SunOS5_7__) || defined(__SunOS5_8__) || defined(__SunOS5_10__)
/* NOT USING #define __MAKECONTEXT_V2_SOURCE 1 / * SunOS */
# else
# define __MAKECONTEXT_V2_SOURCE 1