sandbox: Add support for calling abort()

This function is useful to signal that the application needs to exit
immediate. It can be caught with a debugger (e.g. gdb). Add a stub for it
so that it can be called from within sandbox when an internal error
occurs.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

include/os.h

@@ -351,4 +351,8 @@ int os_setjmp(ulong *jmp, int size);
  */
 void os_longjmp(ulong *jmp, int ret);
 
+/**
+ * os_abort() - Raise SIGABRT to exit sandbox (e.g. to debugger)
+ */
+void os_abort(void);
 #endif