Kea build with perfdhcp enabled fails

name: Bug report
about: Kea build with perfdhcp enabled fails

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Describe the bug

Kea build from source with perfdhcp enabled fails in /kea/src/bin/perfdhcp/test_controll.cc:1016 with error:

make[5]: Entering directory '/kea/src/bin/perfdhcp'
  CXX      test_control.lo
test_control.cc: In member function 'void isc::perfdhcp::TestControl::runWrapped(bool) const':
test_control.cc:1016:24: error: missing sentinel in function call [-Werror=format=]
                    NULL);

To Reproduce Dockerfile

FROM alpine
ENV LOG4CPLUS_VERSION=REL_2_0_2
ENV KEA_VERSION=600677b8111c1940f774c87d35b5c76efdbe1531

RUN apk add --no-cache --virtual .build-deps \
        autoconf \
        automake \
        git \
        libtool \
        build-base \
        boost-dev \
        mysql-dev \
    && \
    git clone --branch $LOG4CPLUS_VERSION --depth 1 --recursive https://github.com/log4cplus/log4cplus.git \
    && \
        cd /log4cplus && \
            ./configure && \
            make -j 4 && \
            make install \
    && \
    git clone https://gitlab.isc.org/isc-projects/kea.git /kea \
    && \
        cd /kea && git checkout $KEA_VERSION && \
            autoreconf --install && \
            ./configure --enable-static-link --with-mysql --enable-perfdhcp && \
            make -j 4 && \
            make install \
    && rm -rf /kea /log4cplus && \
    apk del .build-deps

Expected behavior Build should succeed

Environment:

• alpine image: caf27325b298
• Kea git commit: 600677b8
• gcc version: 8.3.0

Describe the solution you'd like

diff --git a/src/bin/perfdhcp/test_control.cc b/src/bin/perfdhcp/test_control.cc
index 9ae1e9dd45..edd65900cf 100644
--- a/src/bin/perfdhcp/test_control.cc
+++ b/src/bin/perfdhcp/test_control.cc
@@ -1013,7 +1013,7 @@ TestControl::runWrapped(bool do_stop /*= false */) const {
         } else if (pid == 0) {
             execlp(options_.getWrapped().c_str(),
                    do_stop ? "stop" : "start",
-                   NULL);
+                   (void *)NULL);
         }
     }
 }