package/domoticz: fix build with cmake < 3.16

Disable precompiled header because it needs cmake >= 3.16 since version
2020.1 and
https://github.com/domoticz/domoticz/commit/2430e5c85624139dd15a74267d6e50992e394509

Fixes:
 - http://autobuild.buildroot.org/results/7c6e5cb35dffa142972ad19594c8cc092cbfaa76

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
[yann.morin.1998@free.fr:
  - first assignment to CONF_OPTS, so use '=', not '+='
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/domoticz/domoticz.mk

@@ -19,6 +19,9 @@ DOMOTICZ_DEPENDENCIES = \
 	sqlite \
 	zlib
 
+# Disable precompiled header as it needs cmake >= 3.16
+DOMOTICZ_CONF_OPTS = -DUSE_PRECOMPILED_HEADER=OFF
+
 # Due to the dependency on mosquitto, domoticz depends on
 # !BR2_STATIC_LIBS so set USE_STATIC_BOOST and USE_OPENSSL_STATIC to OFF
 DOMOTICZ_CONF_OPTS += \