current master not building on ubuntu 16.04 using --with-libtool --enable-developer

the build fails with the following:

libtool: compile:  gcc -I/home/jenkins/workspace/bind9-master-ubuntu1604-amd64 -I../../.. -I./include -I./../pthreads/include -I../include -I./../include -I./.. -I/usr/include -I/home/jenkins/workspace/bind9-master-ubuntu1604-amd64/unit/atf/include -DISC_MEM_DEFAULTFILL=1 -DISC_LIST_CHECKINIT=1 -DNS_HOOKS_ENABLE=1 -D_GNU_SOURCE -DNS_HOOKS_ENABLE=1 -g -O2 -pthread -I/usr/include/libxml2 -fPIC -W -Wall -Wmissing-prototypes -Wcast-qual -Wwrite-strings -Wformat -Wpointer-arith -fno-strict-aliasing -fno-delete-null-pointer-checks -Wshadow -Werror -c app.c  -fPIC -DPIC -o .libs/app.o
app.c: In function ‘isc__app_ctxstart’:
app.c:305:3: error: ignoring return value of ‘strerror_r’, declared with attribute warn_unused_result [-Werror=unused-result]
   strerror_r(errno, strbuf, sizeof(strbuf));
   ^
app.c:313:3: error: ignoring return value of ‘strerror_r’, declared with attribute warn_unused_result [-Werror=unused-result]
   strerror_r(presult, strbuf, sizeof(strbuf));
   ^
app.c: In function ‘handle_signal’:
app.c:184:3: error: ignoring return value of ‘strerror_r’, declared with attribute warn_unused_result [-Werror=unused-result]
   strerror_r(errno, strbuf, sizeof(strbuf));
   ^
app.c: In function ‘isc__app_ctxrun’:
app.c:505:5: error: ignoring return value of ‘strerror_r’, declared with attribute warn_unused_result [-Werror=unused-result]
     strerror_r(errno, strbuf, sizeof(strbuf));
     ^
app.c: In function ‘isc__app_ctxshutdown’:
app.c:586:6: error: ignoring return value of ‘strerror_r’, declared with attribute warn_unused_result [-Werror=unused-result]
      strerror_r(result,
      ^
app.c: In function ‘isc__app_ctxsuspend’:
app.c:659:6: error: ignoring return value of ‘strerror_r’, declared with attribute warn_unused_result [-Werror=unused-result]
      strerror_r(result,
      ^
cc1: all warnings being treated as errors
Makefile:172: recipe for target 'app.lo' failed
make[3]: *** [app.lo] Error 1