package/xscreensaver: fix linking with intl

xscreensaver doesn't build with (e)glibc toolchain when gettext package is
selected.

With (e)glibc libintl is provided by the libc whereas with uClibc it's provided
by gettext.

If "LIBS=-lintl" is removed from XSCREENSAVER_CONF_ENV, then the -lintl is
missing during xscreensaver build if the toolchain needs gettext.

xscreensaver.o: In function `main':
undefined reference to `libintl_bindtextdomain'
undefined reference to `libintl_textdomain'

Backport a patch applied in 5.28 that fix linking issue with intl and remove
"LIBS=-lintl" from XSCREENSAVER_CONF_ENV.

Note:
gettext package is always selected with xscreensaver when BR2_NEEDS_GETTEXT is
set due to dependencies on libgtk2 and libglib2.

Fixes:
http://autobuild.buildroot.net/results/39b/39b6ad07ad59d87afeca6e427c69f580bed35700/build-end.log



Signed-off-by: Romain Naour <romain.naour@openwide.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>