Allow z/OS to work in either EBCDIC or ASCII mode

IBM has an initiative underway to port various open source projects to
work on z/OS, running under ASCII.  But its native character set is IBM
1047.  This requires a bunch of fancy footwork that they have
undertaken.  One of the necessary things is to be able to set the
character set of a file descriptor.  The __setfdccsid() function does
that, but it and its header file, zos.h, are only defined in ASCII
builds.  This commit allows perl to work in both modes.

os390/os390.c

@@ -11,7 +11,6 @@
 #include <fcntl.h>
 #include <libgen.h>
 #include <termios.h>
-#include <zos.h>
 #include "EXTERN.h"
 #include "perl.h"
 #include "XSUB.h"

perl.h

@@ -4470,7 +4470,16 @@ intrinsic function, see its documents for more details.
 #endif
 
 #if defined(__CYGWIN__) || defined(__MVS__)
+
 void init_os_extras(void);
+
+#endif
+#if defined(__MVS__)
+#  ifdef EBCDIC
+#    define __setfdccsid(to_fd,  bits)  0
+#  else
+#    include <zos.h>
+#  endif
 #endif
 
 union any {