libc: Provide ucontext_t/mcontext_t/<sys/ucontext.h>

This patch updates the C library headers to provide ucontext_t
definitions for three architectures.

+ Fix <signal.h> to always define 'struct sigcontext'.

The new declarations are announced with new macros defined in
<sys/cdefs.h> in order to make it easier to adapt client code
that already defines its own, incompatible, versions of the
structures seen here.

http://code.google.com/p/android/issues/detail?id=34784

Change-Id: Ie78c48690a4ce61c50593f6c39639be7fead3596

libc/include/sys/cdefs.h

@@ -510,4 +510,12 @@
 #define __BIONIC_FORTIFY_UNKNOWN_SIZE ((size_t) -1)
 #endif
 
+/* Indicates to client code that <signal.h> now defines 'struct sigcontext'
+ * properly. See comments in <signal.h> */
+#define __BIONIC_HAVE_STRUCT_SIGCONTEXT  1
+
+/* Indicates to client code that <signal.h> now defines 'ucontext_t' */
+/* NOTE: That does not mean that <ucontext.h> is available! */
+#define __BIONIC_HAVE_UCONTEXT_T  1
+
 #endif /* !_SYS_CDEFS_H_ */

libc/include/sys/ucontext.h

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+#ifndef _SYS_UCONTEXT_H_
+#define _SYS_UCONTEXT_H_
+
+/* While not standard, this header is typically provided by GLibc and the
+ * BSD C library to provide for the definition of ucontext_t and mcontext_t,
+ * without the declarations of the deprecated *context() functions in
+ * <ucontext.h>.
+ *
+ * Client code that directly includes this file exists. Note that
+ * the better, POSIX-compliant, way to get these declarations is to include
+ * <signal.h>.
+ */
+
+#include <machine/ucontext.h>
+
+#endif /* _SYS_UCONTEXT_H_ */