clamav: add libiconv dependencies when build with NLS

clamav: add libiconv dependencies when build with NLS

NLS means Native Language Support and when you have it enabled (it is
not default), clamav can not be compiled as it shows following error:

Package clamav is missing dependencies for the following libraries:
libiconv.so.2

Also, it is required that package libiconv-full is compiled first/before
than clamav and then try to compile clamav.

Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
(cherry picked from commit 87be6ffe6076778336f7db752fee0ef5f3f923e8)