Use ucontext_t not struct ucontext in linux-unwind.h files.
Current glibc no longer gives the ucontext_t type the tag struct
ucontext, to conform with POSIX namespace rules. This requires
various linux-unwind.h files in libgcc, that were previously using
struct ucontext, to be fixed to use ucontext_t instead. This is
similar to the removal of the struct siginfo tag from siginfo_t some
years ago.
Backport of patches by Joseph Myers, taken from
https://gcc.gnu.org/viewcvs/gcc?limit_changes=0&view=revision&revision=249957
[YOCTO #12083]
Signed-off-by: Juro Bystricky <juro.bystricky@intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
