package/libmodsecurity: fix static build

package/libmodsecurity: fix static build

Fix the following static build failure with nginx raised since bump of
libmodsecurity to version 3.0.5 in commit
464d0be380c84ac7c3f1684e49153c3868280d7e:

/home/buildroot/autobuild/instance-2/output-1/host/lib/gcc/xtensa-buildroot-linux-uclibc/10.3.0/../../../../xtensa-buildroot-linux-uclibc/bin/ld: /home/buildroot/autobuild/instance-2/output-1/host/bin/../xtensa-buildroot-linux-uclibc/sysroot/usr/lib/libmodsecurity.a(libmodsecurity_la-transaction.o): in function `std::basic_streambuf<char, std::char_traits<char> >::sbumpc() [clone .isra.0]':
transaction.cc:(.text+0x40): undefined reference to `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_dispose()'

Fixes:
 - http://autobuild.buildroot.org/results/e5a9eb8448980f1c5cafe97180b7d1f48ddf02ca

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>