Remove configure probe for link.

link() is in SUSv2 and all targeted Unix systems have it.  We have
replacement code for Windows that doesn't require a configure probe.
Since only Windows needs it, rename src/port/link.c to win32link.c like
other similar things.

There is no need for a vestigial HAVE_LINK macro, because we expect all
Unix and, with our replacement function, Windows systems to have it, so
we didn't have any tests around link() usage.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA+hUKGJ3LHeP9w5Fgzdr4G8AnEtJ=z=p6hGDEm4qYGEUX5B6fQ@mail.gmail.com

src/include/pg_config.h.in

@@ -334,9 +334,6 @@
 /* Define to 1 if you have the `zstd' library (-lzstd). */
 #undef HAVE_LIBZSTD
 
-/* Define to 1 if you have the `link' function. */
-#undef HAVE_LINK
-
 /* Define to 1 if the system has the type `locale_t'. */
 #undef HAVE_LOCALE_T
 

src/include/port.h

@@ -402,7 +402,8 @@ extern float pg_strtof(const char *nptr, char **endptr);
 #define strtof(a,b) (pg_strtof((a),(b)))
 #endif
 
-#ifndef HAVE_LINK
+#ifdef WIN32
+/* src/port/win32link.c */
 extern int	link(const char *src, const char *dst);
 #endif
 

src/port/win32link.c

@@ -1,21 +1,19 @@
 /*-------------------------------------------------------------------------
  *
- * link.c
+ * win32link.c
  *
  * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  *
  * IDENTIFICATION
- *	  src/port/link.c
+ *	  src/port/win32link.c
  *
  *-------------------------------------------------------------------------
  */
 
 #include "c.h"
 
-#ifdef WIN32
-
 int
 link(const char *src, const char *dst)
 {
@@ -31,5 +29,3 @@ link(const char *src, const char *dst)
 	else
 		return 0;
 }
-
-#endif

src/tools/msvc/Mkvcbuild.pm

@@ -103,13 +103,15 @@ sub mkvcbuild
 	  getpeereid.c getrusage.c inet_aton.c
 	  getaddrinfo.c gettimeofday.c inet_net_ntop.c kill.c open.c
 	  snprintf.c strlcat.c strlcpy.c dirmod.c noblock.c path.c
-	  dirent.c getopt.c getopt_long.c link.c
+	  dirent.c getopt.c getopt_long.c
 	  pread.c preadv.c pwrite.c pwritev.c pg_bitutils.c
 	  pg_strong_random.c pgcheckdir.c pgmkdirp.c pgsleep.c pgstrcasecmp.c
 	  pqsignal.c mkdtemp.c qsort.c qsort_arg.c bsearch_arg.c quotes.c system.c
 	  strerror.c tar.c
 	  win32dlopen.c
-	  win32env.c win32error.c win32ntdll.c
+	  win32env.c win32error.c
+	  win32link.c
+	  win32ntdll.c
 	  win32security.c win32setlocale.c win32stat.c);
 
 	push(@pgportfiles, 'strtof.c') if ($vsVersion < '14.00');

src/tools/msvc/Solution.pm

@@ -306,7 +306,6 @@ sub GenerateFiles
 		HAVE_LIBXSLT                                => undef,
 		HAVE_LIBZ                   => $self->{options}->{zlib} ? 1 : undef,
 		HAVE_LIBZSTD                => undef,
-		HAVE_LINK                   => undef,
 		HAVE_LOCALE_T               => 1,
 		HAVE_LONG_INT_64            => undef,
 		HAVE_LONG_LONG_INT_64       => 1,