Put back ucontext.h, but omit function prototypes for getcontext(),

makecontext(), setcontext(), and swapcontext() which are marked as
obsolescent by SuSv3, and are not implemented by uClibc.

include/ucontext.h

@@ -0,0 +1,32 @@
+/* Copyright (C) 1997, 1998, 1999, 2000 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#ifndef _UCONTEXT_H
+#define _UCONTEXT_H	1
+
+#include <features.h>
+
+/* Get machine dependent definition of data structures.  */
+#include <sys/ucontext.h>
+
+/* The System V ABI user-level context switching support functions
+ * are marked obsolescent by SuSv3, and are not implemented by
+ * uClibc.  This header is therefore empty.  */
+
+
+#endif /* ucontext.h */