gh-85984: Add _POSIX_VDISABLE from unistd.h to termios module. (#114985)

Signed-off-by: Soumendra Ganguly <soumendraganguly@gmail.com>
Co-authored-by: Gregory P. Smith <greg@krypto.org>

Author: 8vasu

Misc/NEWS.d/next/Library/2024-02-04-02-28-37.gh-issue-85984.NHZVTQ.rst

@@ -0,0 +1 @@
+Added ``_POSIX_VDISABLE`` from C's ``<unistd.h>`` to :mod:`termios`.

Modules/termios.c

@@ -27,9 +27,7 @@
 
 #include <termios.h>
 #include <sys/ioctl.h>
-#if defined(__sun) && defined(__SVR4)
-#  include <unistd.h>             // ioctl()
-#endif
+#include <unistd.h> // _POSIX_VDISABLE
 
 /* HP-UX requires that this be included to pick up MDCD, MCTS, MDSR,
  * MDTR, MRI, and MRTS (apparently used internally by some things
@@ -1315,6 +1313,9 @@ static struct constant {
 #ifdef TIOCTTYGSTRUCT
     {"TIOCTTYGSTRUCT", TIOCTTYGSTRUCT},
 #endif
+#ifdef _POSIX_VDISABLE
+    {"_POSIX_VDISABLE", _POSIX_VDISABLE},
+#endif
 
     /* sentinel */
     {NULL, 0}