support cross-compile for linux-os.

Signed-off-by: Bian Naimeng <biannm@cn.fujitsu.com>

diff -Nurp ctdb-2.5.1.orig/configure ctdb-2.5.1/configure
--- ctdb-2.5.1.orig/configure	2015-05-07 16:24:28.545000238 +0900
+++ ctdb-2.5.1/configure	2015-05-07 16:28:20.894000244 +0900
@@ -10692,10 +10692,16 @@ if test x"$libreplace_cv_HAVE_GETADDRINF
 	# see bug 5910, use our replacements if we detect
 	# a broken system.
 	if test "$cross_compiling" = yes; then :
+		case "$target_os" in
+		*linux*)
+			;;
+		*)
   { { $as_echo "$as_me:${as_lineno-$LINENO}: error: in \`$ac_pwd':" >&5
 $as_echo "$as_me: error: in \`$ac_pwd':" >&2;}
 as_fn_error $? "cannot run test program while cross compiling
 See \`config.log' for more details" "$LINENO" 5; }
+			;;
+		esac
 else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */