[Ada] Include errno.h in QNX specific part of the signal handling

[Pierre-Marie de Rodat via Gcc-patches]

To get access to the errno variable, we need to include errno.h.

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

gcc/ada/

        * init.c (QNX): Add #include errno.h.
diff --git a/gcc/ada/init.c b/gcc/ada/init.c
--- a/gcc/ada/init.c
+++ b/gcc/ada/init.c
@@ -2551,6 +2551,7 @@ __gnat_install_handler (void)
 #include <signal.h>
 #include <unistd.h>
 #include <string.h>
+#include <errno.h>
 #include "sigtramp.h"
 
 void