package/log4cxx: needs boost or C++17

log4cxx needs boost or C++17 since bump to version 0.12.0 in
commit 83a0e8de (see
https://github.com/apache/logging-log4cxx/commit/2ab3b78b9aa36524287764a129fa6ad96e89ca02):

In file included from /home/buildroot/autobuild/instance-3/output-1/build/log4cxx-0.12.0/src/main/cpp/action.cpp:18:0:
/home/buildroot/autobuild/instance-3/output-1/build/log4cxx-0.12.0/src/main/include/log4cxx/rolling/action.h:51:8: error: 'mutex' in namespace 'std' does not name a type
   std::mutex mutex;
        ^

Fixes:
 - http://autobuild.buildroot.org/results/71e/71eb8c4f69a2505242b3224bd79f4a96eb3b68a4/build-end.log



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>