clamav: add patch to fix build failure caused by lack of libcurl

clamav: add patch to fix build failure caused by lack of libcurl

When json-c is enabled but libcurl is disabled, clamav tries to build
the clamsubmit program, which fails with:

  CC       clamsubmit.o
clamsubmit.c:6:23: fatal error: curl/curl.h: No such file or directory
 #include <curl/curl.h>

This is due to an incorrect curl-config detection logic, leading to
/bin/curl-config being present making the configure script believe
that curl is available, even when --without-libcurl is explicitly
passed.

This commit adds a patch, submitted upstream, which fixes this
problem.

Fixes:

  http://autobuild.buildroot.net/results/c43d2ebd8ab30016969d642dbd71c297dc5f6bab/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>