Convert some long lists in configure.in to one-line-per-entry style.

The idea here is that patches that add items to these lists will often
be easier to rebase over other additions to the same lists, because
they won't be trying to touch the very same line of configure.in.

There will still be merge conflicts in the configure script, but that
can be fixed just by re-running autoconf (or by leaving configure out
of the submitted patch to begin with ...)

Implementation note: use of m4_normalize() is necessary to get rid of
the newlines, else incorrect shell syntax will be emitted.  But with
that hack, the generated configure script is identical to what it
was before.

Discussion: https://postgr.es/m/19344.1539050134@sss.pgh.pa.us

configure.in

@@ -1292,7 +1292,34 @@ AC_SUBST(UUID_LIBS)
 
 AC_HEADER_STDBOOL
 
-AC_CHECK_HEADERS([atomic.h crypt.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h mbarrier.h poll.h sys/epoll.h sys/ipc.h sys/prctl.h sys/procctl.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/sockio.h sys/tas.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h])
+AC_CHECK_HEADERS(m4_normalize([
+	atomic.h
+	crypt.h
+	fp_class.h
+	getopt.h
+	ieeefp.h
+	ifaddrs.h
+	langinfo.h
+	mbarrier.h
+	poll.h
+	sys/epoll.h
+	sys/ipc.h
+	sys/prctl.h
+	sys/procctl.h
+	sys/pstat.h
+	sys/resource.h
+	sys/select.h
+	sys/sem.h
+	sys/shm.h
+	sys/sockio.h
+	sys/tas.h
+	sys/un.h
+	termios.h
+	ucred.h
+	utime.h
+	wchar.h
+	wctype.h
+]))
 
 # On BSD, test for net/if.h will fail unless sys/socket.h
 # is included first.
@@ -1571,7 +1598,32 @@ PGAC_FUNC_WCSTOMBS_L
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-AC_CHECK_FUNCS([cbrt clock_gettime fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll posix_fallocate ppoll pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open strchrnul symlink sync_file_range utime utimes wcstombs_l])
+AC_CHECK_FUNCS(m4_normalize([
+	cbrt
+	clock_gettime
+	fdatasync
+	getifaddrs
+	getpeerucred
+	getrlimit
+	mbstowcs_l
+	memmove
+	poll
+	posix_fallocate
+	ppoll
+	pstat
+	pthread_is_threaded_np
+	readlink
+	setproctitle
+	setproctitle_fast
+	setsid
+	shm_open
+	strchrnul
+	symlink
+	sync_file_range
+	utime
+	utimes
+	wcstombs_l
+]))
 
 AC_REPLACE_FUNCS(fseeko)
 case $host_os in
@@ -1640,7 +1692,21 @@ else
   AC_CHECK_FUNCS([fpclass fp_class fp_class_d class], [break])
 fi
 
-AC_REPLACE_FUNCS([crypt dlopen fls getopt getrusage inet_aton mkdtemp random rint srandom strlcat strlcpy strnlen])
+AC_REPLACE_FUNCS(m4_normalize([
+	crypt
+	dlopen
+	fls
+	getopt
+	getrusage
+	inet_aton
+	mkdtemp
+	random
+	rint
+	srandom
+	strlcat
+	strlcpy
+	strnlen
+]))
 
 case $host_os in