package/clamav: fix static build

clamav unconditionally includes dlfcn.h which is missing on a uClibc
that is configured as a pure-static C library.

Thus, the build fails.

But the including file does not even makes use of any function from the
dlopen() familly, so it does not need to include dlfcn.h to start with.

Add a patch to clamav to not include dlfcn.h where not needed.

Fixes:
    http://autobuild.buildroot.net/results/b49/b491f4e5e1760248adb8d21b404e8aa15f7dbdd1/



[Peter: fix typo in patch description]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>