This is a forward-compatibility patch used to avoid two problems:
1/ The C library <signal.h> is going to be updated to define 'struct sigcontext'
properly soon. Avoid redefining this structure here when it's not really needed
to prevent a type conflict.
2/ Similarly, proper ucontext_t support is going to be added, prevent conflict by
using a macro renaming trick. Mainly because there is a slight chance that the
C library definition will follow a slightly different layout/naming.
For context, see details at:
http://code.google.com/p/android/issues/detail?id=34784https://android-review.googlesource.com/#/c/38875/1
Change-Id: Ie94eb5d77297f8e0bafd146b65a648bd8805a551
b4ef91b975