dropwatch: link with libintl if present

binutils libbfd links to libintl if present, so dropwatch needs it too.
Ugly hardcoded LDFLAGS, but then that's what the dropwatch Makefile
does. Fixes:
http://autobuild.buildroot.net/results/549/54917e7943143e47263b60b4eee3dfc6f0801407/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>