package/clamav: needs libtool

package/clamav: needs libtool

clamav contains a copy of libltdl which is used when the libtool
package is not present, this increases the filesize of the target libs:

linked against libltdl.so:

-rwxr-xr-x 1 bernd bernd 1838528 Mär 11 13:21 output/target/usr/lib/libclamav.so.7.1.1

$ output/host/usr/bin/i586-buildroot-linux-uclibc-readelf -a output/target/usr/lib/libclamav.so.7.1.1 | grep NEEDED
 0x00000001 (NEEDED)                     Shared library: [libltdl.so.7]
 0x00000001 (NEEDED)                     Shared library: [libssl.so.1.0.0]
 0x00000001 (NEEDED)                     Shared library: [libcrypto.so.1.0.0]
 0x00000001 (NEEDED)                     Shared library: [libz.so.1]
 0x00000001 (NEEDED)                     Shared library: [libc.so.0]

not linked against libltdl.so:

-rwxr-xr-x 1 bernd bernd 1859548 Mär 11 13:21 output/target/usr/lib/libclamav.so.7.1.1

$ output/host/usr/bin/i586-buildroot-linux-uclibc-readelf -a output/target/usr/lib/libclamav.so.7.1.1 | grep NEEDED
 0x00000001 (NEEDED)                     Shared library: [libssl.so.1.0.0]
 0x00000001 (NEEDED)                     Shared library: [libcrypto.so.1.0.0]
 0x00000001 (NEEDED)                     Shared library: [libz.so.1]
 0x00000001 (NEEDED)                     Shared library: [libc.so.0]

Therefore this patch adds libtool as hard dependency to clamav.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>