patch 8.1.0766: various problems when using Vim on VMS

Problem:    Various problems when using Vim on VMS.
Solution:   Various fixes. Define long_long_T. (Zoltan Arpadffy)
diff --git a/src/gui_xmebw.c b/src/gui_xmebw.c
index b09b1e6..cd60794 100644
--- a/src/gui_xmebw.c
+++ b/src/gui_xmebw.c
@@ -35,7 +35,13 @@
 # include <Xm/XpmP.h>
 # define UNHIGHLIGHTT
 #else
-# include <X11/xpm.h>
+# ifdef HAVE_X11_XPM_H
+#  ifdef VMS
+#   include <xpm.h>
+#  else
+#   include <X11/xpm.h>
+#  endif
+# endif
 #endif
 #include <Xm/ManagerP.h>
 #include <Xm/Display.h>