On x86_64, RtlCaptureContext() uses fxsave to save FPU/MMX/SSE state.
fxsave requires that the destination address is 16-byte aligned, or it will
fault.
CONTEXT is already annotated __attribute__ ((aligned (16))), do the same with
struct _mcontext.
Rearrange ucontext_t so that it's struct _mcontext element is also correctly
aligned.
* include/cygwin/signal.h (struct __mcontext): 16-byte align.
* include/sys/ucontext.h (ucontext_t): Ditto.
Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>
383ff5fc47