Not buildable on OpenWRT

Not buildable on OpenWRT 4.2.2 won't build on OpenWRT because it's not finding <isc/boolean.h>.

To Reproduce Steps to reproduce the behavior:

Checkout master on openwrt/packages, and change net/isc-dhcp/Makefile to use version 4.4.2.
Build
See error

Expected behavior It should build as 4.4.1 did.

Environment:

ISC DHCP version: 4.4.2
OS: OpenWRT master cross-built on Ubuntu 20.04.02 LTS
CONFIG_PACKAGE_isc-dhcp-server-ipv6=y should be configured

Additional Information Build fails as:

make[5]: Entering directory '/home/philipp/lede/build_dir/target-x86_64_musl/isc-dhcp-ipv6/dhcp-4.4.2/common'
x86_64-openwrt-linux-musl-gcc -DHAVE_CONFIG_H -I. -I../includes  -I.. -DLOCALSTATEDIR='"/var"' -I/home/philipp/lede/staging_dir/toolchain-x86_64_gcc-8.4.0_musl/usr/include -I/home/philipp/lede/staging_dir/toolchain-x86_64_gcc-8.4.0_musl/include/fortify -I/home/philipp/lede/staging_dir/toolchain-x86_64_gcc-8.4.0_musl/include   -Os -pipe -fno-caller-saves -fno-plt -fhonour-copts -Wno-error=unused-but-set-variable -Wno-error=unused-result -fmacro-prefix-map=/home/philipp/lede/build_dir/target-x86_64_musl/isc-dhcp-ipv6/dhcp-4.4.2=dhcp-4.4.2 -Wformat -Werror=format-security -fstack-protector -D_FORTIFY_SOURCE=1 -Wl,-z,now -Wl,-z,relro -fcommon   -I../includes -I/home/philipp/lede/build_dir/target-x86_64_musl/isc-dhcp-ipv6/dhcp-4.4.2/bind/include -c -o alloc.o alloc.c
In file included from ../includes/dhcpd.h:91,
                 from alloc.c:29:
../includes/omapip/isclib.h:51:10: fatal error: isc/boolean.h: No such file or directory
 #include <isc/boolean.h>
          ^~~~~~~~~~~~~~~
compilation terminated.
make[5]: *** [Makefile:504: alloc.o] Error 1
make[5]: Leaving directory '/home/philipp/lede/build_dir/target-x86_64_musl/isc-dhcp-ipv6/dhcp-4.4.2/common'
make[4]: *** [Makefile:563: all-recursive] Error 1
make[4]: Leaving directory '/home/philipp/lede/build_dir/target-x86_64_musl/isc-dhcp-ipv6/dhcp-4.4.2/common'
make[3]: *** [Makefile:464: all-recursive] Error 1
make[3]: Leaving directory '/home/philipp/lede/build_dir/target-x86_64_musl/isc-dhcp-ipv6/dhcp-4.4.2'
make[2]: *** [Makefile:301: /home/philipp/lede/build_dir/target-x86_64_musl/isc-dhcp-ipv6/dhcp-4.4.2/.built] Error 2
make[2]: Leaving directory '/home/philipp/lede/feeds/packages/net/isc-dhcp'
time: package/feeds/packages/isc-dhcp/ipv6/compile#93.82#21.71#108.97
    ERROR: package/feeds/packages/isc-dhcp failed to build (build variant: ipv6).
make[1]: *** [package/Makefile:114: package/feeds/packages/isc-dhcp/compile] Error 1