Re-order configure tests to reflect the fact that the code generated for

posix_fadvise and other file-related functions can depend on _LARGEFILE_SOURCE
and/or _FILE_OFFSET_BITS.  Per report from Robert Treat.

Back-patch to 8.4.  This has been wrong all along, but we weren't really using
posix_fadvise in anger before, and AC_FUNC_FSEEKO seems to mask the issue well
enough for that function.

configure.in

@@ -1,5 +1,5 @@
 dnl Process this file with autoconf to produce a configure script.
-dnl $PostgreSQL: pgsql/configure.in,v 1.620 2010/01/07 03:24:57 tgl Exp $
+dnl $PostgreSQL: pgsql/configure.in,v 1.621 2010/01/16 19:50:26 tgl Exp $
 dnl
 dnl Developers, please strive to achieve this order:
 dnl
@@ -1144,6 +1144,20 @@ AC_MSG_RESULT(yes)],
               [AC_MSG_RESULT(no)])
 fi
 
+# Check largefile support.  You might think this is a system service not a
+# compiler characteristic, but you'd be wrong.  We must check this before
+# probing existence of related functions such as fseeko, since the largefile
+# defines can affect what is generated for that.
+AC_SYS_LARGEFILE
+
+# Check for largefile support (must be after AC_SYS_LARGEFILE)
+AC_CHECK_SIZEOF([off_t])
+
+# If we don't have largefile support, can't handle segsize >= 2GB.
+if test "$ac_cv_sizeof_off_t" -lt 8 -a "$segsize" != "1"; then 
+   AC_MSG_ERROR([Large file support is not enabled. Segment size cannot be larger than 1GB.]) 
+fi
+
 
 ##
 ## Functions, global variables
@@ -1155,6 +1169,17 @@ PGAC_FUNC_GETTIMEOFDAY_1ARG
 
 AC_CHECK_FUNCS([cbrt dlopen fcvt fdatasync getifaddrs getpeereid getpeerucred getrlimit memmove poll pstat readlink setproctitle setsid sigprocmask symlink sysconf towlower utime utimes waitpid wcstombs])
 
+AC_REPLACE_FUNCS(fseeko)
+case $host_os in
+	# BSD/OS & NetBSD use a custom fseeko/ftello built on fsetpos/fgetpos
+	# Mingw uses macros to access Win32 API calls
+	bsdi*|netbsd*|mingw*)
+		AC_DEFINE(HAVE_FSEEKO, 1, [Define to 1 because replacement version used.])
+		ac_cv_func_fseeko=yes;;
+	*)
+		AC_FUNC_FSEEKO;;
+esac
+
 # posix_fadvise() is a no-op on Solaris, so don't incur function overhead
 # by calling it, 2009-04-02
 # http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/lib/libc/port/gen/posix_fadvise.c
@@ -1367,17 +1392,6 @@ AC_CHECK_FUNCS(atexit, [],
                [AC_CHECK_FUNCS(on_exit, [],
                [AC_MSG_ERROR([neither atexit() nor on_exit() found])])])
 
-AC_REPLACE_FUNCS(fseeko)
-case $host_os in
-	# BSD/OS & NetBSD use a custom fseeko/ftello built on fsetpos/fgetpos
-	# Mingw uses macros to access Win32 API calls
-	bsdi*|netbsd*|mingw*)
-		AC_DEFINE(HAVE_FSEEKO, 1, [Define to 1 because replacement version used.])
-		ac_cv_func_fseeko=yes;;
-	*)
-		AC_FUNC_FSEEKO;;
-esac
-
 
 #
 # Pthreads
@@ -1651,18 +1665,6 @@ operating system;  use --disable-thread-safety to disable thread safety.])
 fi
 fi
 
-if test $ac_cv_func_fseeko = yes; then
-AC_SYS_LARGEFILE
-fi
-
-# Check for largefile support (must be after AC_SYS_LARGEFILE)
-AC_CHECK_SIZEOF([off_t])
-
-# If we don't have largefile support, can't handle segsize >= 2GB.
-if test "$ac_cv_sizeof_off_t" -lt 8 -a "$segsize" != "1"; then 
-   AC_MSG_ERROR([Large file support is not enabled. Segment size cannot be larger than 1GB.]) 
-fi
-
 # SunOS doesn't handle negative byte comparisons properly with +/- return
 AC_FUNC_MEMCMP