pythongh-63760: Don't declare gethostname() on Solaris (python#108817)

Since 2005, Solaris defines gethostname(). socketmodule.c no longer
has to define gethostname() for Solaris.

Oracle Solaris and OpenSolaris have patches to remove the
gethostname() definition in Python:

* /~https://github.com/oracle/solaris-userland/blob/master/components/python/python37/patches/15-gethostname.patch
* /~https://github.com/OpenIndiana/oi-userland/blob/oi/hipster/components/python/python37/patches/15-gethostname.patch
* /~https://github.com/omniosorg/omnios-build/blob/master/build/python27/patches/24-gethostname.patch

Co-authored-by: Jakub Kulík <Kulikjak@gmail.com>
(cherry picked from commit 0e6d582)

Include/pyport.h

@@ -429,11 +429,6 @@ Please be conservative with adding new ones, document them and enclose them
 in platform-specific #ifdefs.
 **************************************************************************/
 
-#ifdef SOLARIS
-/* Unchecked */
-extern int gethostname(char *, int);
-#endif
-
 #ifdef HAVE__GETPTY
 #include <sys/types.h>          /* we need to import mode_t */
 extern char * _getpty(int *, int, mode_t, int);

Misc/NEWS.d/next/Build/2023-09-02-18-04-15.gh-issue-63760.r8hJ6q.rst

@@ -0,0 +1,3 @@
+Fix Solaris build: no longer redefine the ``gethostname()`` function. Solaris
+defines the function since 2005. Patch by Victor Stinner, original patch by
+Jakub Kulík.