[Ada] sysdep.c: correct include directives ordering

Some VxWorks headers are relying on types that are defined in
`vxWorks.h` but do not include it themselves, we move the include
directive for `vxWorks.h` at the top of the include directives.

2019-07-10  Corentin Gay  <gay@adacore.com>

gcc/ada/

	* sysdep.c: Put include directive for 'vxWorks.h' before any
	other VxWorks headers.

From-SVN: r273338

gcc/ada/ChangeLog

+2019-07-10  Corentin Gay  <gay@adacore.com>
+
+	* sysdep.c: Put include directive for 'vxWorks.h' before any
+	other VxWorks headers.
+
 2019-07-10  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* doc/gnat_rm/implementation_defined_attributes.rst

gcc/ada/sysdep.c

@@ -33,6 +33,7 @@
    GNAT Run Time Library */
 
 #ifdef __vxworks
+#include "vxWorks.h"
 #include "ioLib.h"
 #if ! defined (VTHREADS)
 #include "dosFsLib.h"
@@ -41,7 +42,6 @@
 # include "nfsLib.h"
 #endif
 #include "selectLib.h"
-#include "vxWorks.h"
 #include "version.h"
 #if defined (__RTP__)
 #  include "vwModNum.h"