compile mosquitto1.4.1, "/mosquitto_internal.h:40:20: fatal error: ares.h: No such file or directory"

Hi,

i want to update the mosquitto broker from 1.4 to 1.4.1, but got a fatal error. it is strange to me, the compile should be ok...
no clues found from google, so could anyone help me here? thanks.

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.../mosquitto-1.4.1 $ make
set -e; for d in lib client src; do make -C ${d}; done
make[1]: Entering directory '/home/pi/projects/leoMatthias/software/Mosquitto_MQTT/mosquitto-1.4.1/lib'
cc -Wall -ggdb -O2 -I. -I.. -I../lib -fPIC -DWITH_TLS -DWITH_TLS_PSK -DWITH_THREADING -DWITH_SOCKS -DWITH_SRV -c mosquitto.c -o mosquitto.o
In file included from mosquitto.c:33:0:
./mosquitto_internal.h:40:20: fatal error: ares.h: No such file or directory
compilation terminated.
Makefile:51: recipe for target 'mosquitto.o' failed
make[1]: *** [mosquitto.o] Error 1
make[1]: Leaving directory '/home/pi/projects/leoMatthias/software/Mosquitto_MQTT/mosquitto-1.4.1/lib'
Makefile:21: recipe for target 'mosquitto' failed
make: *** [mosquitto] Error 2