Remove configure probes for sys/un.h and struct sockaddr_un.

<sys/un.h> is in SUSv3 and every targeted Unix has it.  Some Windows
tool chains may still lack the approximately equivalent header
<afunix.h>, so we already defined struct sockaddr_un ourselves on that
OS for now.  To harmonize things a bit, move our definition into a new
header src/include/port/win32/sys/un.h.

HAVE_UNIX_SOCKETS is now defined unconditionally.  We migh remove that
in a separate commit, pending discussion.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA%2BhUKG%2BL_3brvh%3D8e0BW_VfX9h7MtwgN%3DnFHP5o7X2oZucY9dg%40mail.gmail.com

config/c-library.m4

@@ -76,20 +76,6 @@ AC_DEFUN([PGAC_UNION_SEMUN],
 #endif])])# PGAC_UNION_SEMUN
 
 
-# PGAC_STRUCT_SOCKADDR_UN
-# -----------------------
-# If `struct sockaddr_un' exists, define HAVE_STRUCT_SOCKADDR_UN.
-# If it is missing then one could define it.
-# (Requires test for <sys/un.h>!)
-AC_DEFUN([PGAC_STRUCT_SOCKADDR_UN],
-[AC_CHECK_TYPES([struct sockaddr_un], [], [],
-[#include <sys/types.h>
-#ifdef HAVE_SYS_UN_H
-#include <sys/un.h>
-#endif
-])])# PGAC_STRUCT_SOCKADDR_UN
-
-
 # PGAC_STRUCT_SOCKADDR_STORAGE
 # ----------------------------
 # If `struct sockaddr_storage' exists, define HAVE_STRUCT_SOCKADDR_STORAGE.

configure

@@ -13874,7 +13874,7 @@ $as_echo "#define HAVE_STDBOOL_H 1" >>confdefs.h
 fi
 
 
-for ac_header in atomic.h copyfile.h execinfo.h getopt.h ifaddrs.h langinfo.h mbarrier.h net/if.h netinet/tcp.h sys/epoll.h sys/event.h sys/ipc.h sys/personality.h sys/prctl.h sys/procctl.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/signalfd.h sys/sockio.h sys/ucred.h sys/un.h termios.h ucred.h
+for ac_header in atomic.h copyfile.h execinfo.h getopt.h ifaddrs.h langinfo.h mbarrier.h net/if.h netinet/tcp.h sys/epoll.h sys/event.h sys/ipc.h sys/personality.h sys/prctl.h sys/procctl.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/signalfd.h sys/sockio.h sys/ucred.h termios.h ucred.h
 do :
   as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
 ac_fn_c_check_header_mongrel "$LINENO" "$ac_header" "$as_ac_Header" "$ac_includes_default"
@@ -15117,21 +15117,6 @@ cat >>confdefs.h <<_ACEOF
 _ACEOF
 
 
-fi
-
-ac_fn_c_check_type "$LINENO" "struct sockaddr_un" "ac_cv_type_struct_sockaddr_un" "#include <sys/types.h>
-#ifdef HAVE_SYS_UN_H
-#include <sys/un.h>
-#endif
-
-"
-if test "x$ac_cv_type_struct_sockaddr_un" = xyes; then :
-
-cat >>confdefs.h <<_ACEOF
-#define HAVE_STRUCT_SOCKADDR_UN 1
-_ACEOF
-
-
 fi
 
 ac_fn_c_check_type "$LINENO" "struct sockaddr_storage" "ac_cv_type_struct_sockaddr_storage" "#include <sys/types.h>

configure.ac

@@ -1467,7 +1467,6 @@ AC_CHECK_HEADERS(m4_normalize([
 	sys/signalfd.h
 	sys/sockio.h
 	sys/ucred.h
-	sys/un.h
 	termios.h
 	ucred.h
 ]))
@@ -1625,7 +1624,6 @@ PGAC_C_COMPUTED_GOTO
 PGAC_STRUCT_TIMEZONE
 PGAC_UNION_SEMUN
 AC_CHECK_TYPES(socklen_t, [], [], [#include <sys/socket.h>])
-PGAC_STRUCT_SOCKADDR_UN
 PGAC_STRUCT_SOCKADDR_STORAGE
 PGAC_STRUCT_SOCKADDR_STORAGE_MEMBERS
 PGAC_STRUCT_ADDRINFO

src/include/c.h

@@ -1113,10 +1113,6 @@ extern void ExceptionalCondition(const char *conditionName,
  * ----------------------------------------------------------------
  */
 
-#ifdef HAVE_STRUCT_SOCKADDR_UN
-#define HAVE_UNIX_SOCKETS 1
-#endif
-
 /*
  * Invert the sign of a qsort-style comparison result, ie, exchange negative
  * and positive integer values, being careful not to get the wrong answer

src/include/libpq/pqcomm.h

@@ -17,10 +17,8 @@
 #define PQCOMM_H
 
 #include <sys/socket.h>
-#include <netdb.h>
-#ifdef HAVE_SYS_UN_H
 #include <sys/un.h>
-#endif
+#include <netdb.h>
 #include <netinet/in.h>
 
 #ifdef HAVE_STRUCT_SOCKADDR_STORAGE

src/include/pg_config.h.in

@@ -478,9 +478,6 @@
 /* Define to 1 if `__ss_len' is a member of `struct sockaddr_storage'. */
 #undef HAVE_STRUCT_SOCKADDR_STORAGE___SS_LEN
 
-/* Define to 1 if the system has the type `struct sockaddr_un'. */
-#undef HAVE_STRUCT_SOCKADDR_UN
-
 /* Define to 1 if `tm_zone' is a member of `struct tm'. */
 #undef HAVE_STRUCT_TM_TM_ZONE
 
@@ -538,9 +535,6 @@
 /* Define to 1 if you have the <sys/ucred.h> header file. */
 #undef HAVE_SYS_UCRED_H
 
-/* Define to 1 if you have the <sys/un.h> header file. */
-#undef HAVE_SYS_UN_H
-
 /* Define to 1 if you have the <termios.h> header file. */
 #undef HAVE_TERMIOS_H
 

src/include/port.h

@@ -503,4 +503,7 @@ extern bool wait_result_is_any_signal(int exit_status, bool include_command_not_
 #define HAVE_SYMLINK 1
 #endif
 
+/* Interfaces that we assume that all systems have. */
+#define HAVE_UNIX_SOCKETS 1
+
 #endif							/* PG_PORT_H */

src/include/port/win32.h

@@ -55,14 +55,3 @@
 #ifdef _MSC_VER
 #define PGDLLEXPORT __declspec (dllexport)
 #endif
-
-/*
- * Windows headers don't define this structure, but you can define it yourself
- * to use the functionality.
- */
-struct sockaddr_un
-{
-	unsigned short sun_family;
-	char		sun_path[108];
-};
-#define HAVE_STRUCT_SOCKADDR_UN 1

src/include/port/win32/sys/un.h

@@ -0,0 +1,17 @@
+/*
+ * src/include/port/win32/sys/un.h
+ */
+#ifndef WIN32_SYS_UN_H
+#define WIN32_SYS_UN_H
+
+/*
+ * Windows defines this structure in <afunix.h>, but not all tool chains have
+ * the header yet, so we define it here for now.
+ */
+struct sockaddr_un
+{
+	unsigned short sun_family;
+	char		sun_path[108];
+};
+
+#endif

src/port/getpeereid.c

@@ -16,10 +16,8 @@
 
 #include <sys/param.h>
 #include <sys/socket.h>
-#include <unistd.h>
-#ifdef HAVE_SYS_UN_H
 #include <sys/un.h>
-#endif
+#include <unistd.h>
 #ifdef HAVE_UCRED_H
 #include <ucred.h>
 #endif

src/tools/msvc/Solution.pm

@@ -355,7 +355,6 @@ sub GenerateFiles
 		HAVE_STRUCT_SOCKADDR_STORAGE_SS_LEN      => undef,
 		HAVE_STRUCT_SOCKADDR_STORAGE___SS_FAMILY => undef,
 		HAVE_STRUCT_SOCKADDR_STORAGE___SS_LEN    => undef,
-		HAVE_STRUCT_SOCKADDR_UN                  => undef,
 		HAVE_STRUCT_TM_TM_ZONE                   => undef,
 		HAVE_SYNC_FILE_RANGE                     => undef,
 		HAVE_SYNCFS                              => undef,
@@ -375,7 +374,6 @@ sub GenerateFiles
 		HAVE_SYS_STAT_H                          => 1,
 		HAVE_SYS_TYPES_H                         => 1,
 		HAVE_SYS_UCRED_H                         => undef,
-		HAVE_SYS_UN_H                            => undef,
 		HAVE_TERMIOS_H                           => undef,
 		HAVE_TYPEOF                              => undef,
 		HAVE_UCRED_H                             => undef,