Remove configure probes for poll and poll.h.

poll() and <poll.h> are in SUSv2 and all targeted Unix systems have
them.

Retain HAVE_POLL and HAVE_POLL_H macros for readability.  There's an
error in latch.c that is now unreachable (since we always have one of
WIN32 or HAVE_POLL defined), but that falls out of a decision to keep
using defined(HAVE_POLL) instead of !defined(WIN32) to guard the poll()
code.

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

configure

@@ -13875,7 +13875,7 @@ $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 poll.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/uio.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 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/uio.h sys/un.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" "$ac_includes_default"
@@ -16039,7 +16039,7 @@ fi
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-for ac_func in backtrace_symbols clock_gettime copyfile fdatasync getifaddrs getpeerucred inet_pton kqueue mbstowcs_l memset_s poll posix_fallocate ppoll pthread_is_threaded_np readv setproctitle setproctitle_fast strchrnul strsignal syncfs sync_file_range uselocale wcstombs_l writev
+for ac_func in backtrace_symbols clock_gettime copyfile fdatasync getifaddrs getpeerucred inet_pton kqueue mbstowcs_l memset_s posix_fallocate ppoll pthread_is_threaded_np readv setproctitle setproctitle_fast strchrnul strsignal syncfs sync_file_range uselocale wcstombs_l writev
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"

configure.ac

@@ -1452,7 +1452,6 @@ AC_CHECK_HEADERS(m4_normalize([
 	ifaddrs.h
 	langinfo.h
 	mbarrier.h
-	poll.h
 	sys/epoll.h
 	sys/event.h
 	sys/ipc.h
@@ -1801,7 +1800,6 @@ AC_CHECK_FUNCS(m4_normalize([
 	kqueue
 	mbstowcs_l
 	memset_s
-	poll
 	posix_fallocate
 	ppoll
 	pthread_is_threaded_np

src/include/pg_config.h.in

@@ -376,12 +376,6 @@
 /* Define to 1 if you have the <pam/pam_appl.h> header file. */
 #undef HAVE_PAM_PAM_APPL_H
 
-/* Define to 1 if you have the `poll' function. */
-#undef HAVE_POLL
-
-/* Define to 1 if you have the <poll.h> header file. */
-#undef HAVE_POLL_H
-
 /* Define to 1 if you have the `posix_fadvise' function. */
 #undef HAVE_POSIX_FADVISE
 

src/include/port.h

@@ -532,6 +532,8 @@ extern bool wait_result_is_any_signal(int exit_status, bool include_command_not_
  */
 #ifndef WIN32
 #define HAVE_GETRLIMIT 1
+#define HAVE_POLL 1
+#define HAVE_POLL_H 1
 #define HAVE_READLINK 1
 #define HAVE_SETSID 1
 #define HAVE_SHM_OPEN 1

src/tools/msvc/Solution.pm

@@ -320,8 +320,6 @@ sub GenerateFiles
 		HAVE_OPENSSL_INIT_SSL       => undef,
 		HAVE_OSSP_UUID_H            => undef,
 		HAVE_PAM_PAM_APPL_H         => undef,
-		HAVE_POLL                   => undef,
-		HAVE_POLL_H                 => undef,
 		HAVE_POSIX_FADVISE          => undef,
 		HAVE_POSIX_FALLOCATE        => undef,
 		HAVE_PPC_LWARX_MUTEX_HINT   => undef,