package/lynx: fix build with libidn

In case of BR2_STATIC_LIBS=y the linking with libidn fails because
linker can't resolve libiconv symbols needed by libidn. Fix it by
required LIBS for libidn generated by pkg-conf.

The issue can be reproduced with the following defconfig:

	BR2_x86_i686=y
	BR2_STATIC_LIBS=y
	BR2_PACKAGE_LIBICONV=y
	BR2_PACKAGE_LIBIDN=y
	BR2_PACKAGE_LYNX=y

Fixes:
	http://autobuild.buildroot.net/results/23a421e15c32b17ff2f69f183a2e8620ecb93316/



Signed-off-by: Vadim Kochan <vadim4j@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>