[Ada] qnx-7.1: warning in sigtramp-qnx.c __gnat_sigtramp

[Pierre-Marie de Rodat via Gcc-patches]

Fix compilation warning. The code was using a cast to struct sigcontext
*, which doesn't exist. It worked by accident.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

        * sigtramp-qnx.c: Change struct sigcontext * to mcontext_t *.
diff --git a/gcc/ada/sigtramp-qnx.c b/gcc/ada/sigtramp-qnx.c
--- a/gcc/ada/sigtramp-qnx.c
+++ b/gcc/ada/sigtramp-qnx.c
@@ -49,7 +49,7 @@ void __gnat_sigtramp (int signo, void *si, void *sc,
 void __gnat_sigtramp (int signo, void *si, void *ucontext,
                       __sigtramphandler_t * handler)
 {
-  struct sigcontext *mcontext = &((ucontext_t *) ucontext)->uc_mcontext;
+  mcontext_t *mcontext = &((ucontext_t *) ucontext)->uc_mcontext;
 
   __gnat_sigtramp_common (signo, si, mcontext, handler);
 }