I think there is a series of patches not yet available for ipq806x if I compare it to ipq807x (which was switched to kernel 6.1 as default by @robimarko).
Did you start fresh? Checkout latest master, clean all (make distclean) then build toolchain and firmware?
I did gave it a go yesterday and it compiled without complaining. Do you config using make menuconfig or a saved .config file? What's the git commit you're working with?
This file is missing, do not build for all targets until that is added.
Just build for a specific target e.g. R7800
Edit: I just looked at 23.05-rc1 and it is missing there also it seems
Edit 2: the xr450 seems a software limited xr500 so you can probably get away with just copying the xr500 file e.g.: cp /media/james/D/ipq806x_builds/hnyman/master/build_dir/target-arm_cortex-a15+neon-vfpv4_musl_eabi/linux-ipq806x_generic/linux-6.1.32/arch/arm/boot/dts/qcom-ipq8065-xr500.dts /media/james/D/ipq806x_builds/hnyman/master/build_dir/target-arm_cortex-a15+neon-vfpv4_musl_eabi/linux-ipq806x_generic/linux-6.1.32/arch/arm/boot/dts/qcom-ipq8065-xr450.dts
# Use "make defconfig" to expand this to a full .config
CONFIG_TARGET_ipq806x=y
CONFIG_TARGET_ipq806x_generic=y
CONFIG_TARGET_ipq806x_generic_DEVICE_netgear_r7800=y
#CONFIG_TESTING_KERNEL=y
# Per-package build logs in <buildroot>/logs
CONFIG_DEVEL=y
CONFIG_BUILD_LOG=y
# Debugging options (build gdbserver, include package debug)
CONFIG_PACKAGE_gdbserver=y
CONFIG_DEBUG=y
# Include package list in build
CONFIG_INCLUDE_CONFIG=y
# Longer waiting for failsafe button push
###CONFIG_IMAGEOPT=y
###CONFIG_PREINITOPT=y
###CONFIG_TARGET_PREINIT_TIMEOUT=5
# Busybox tweaks
CONFIG_BUSYBOX_CUSTOM=y
#CONFIG_BUSYBOX_CONFIG_DIFF=y
CONFIG_BUSYBOX_CONFIG_FEATURE_EDITING_SAVEHISTORY=y
CONFIG_BUSYBOX_CONFIG_FEATURE_EDITING_SAVE_ON_EXIT=y
CONFIG_BUSYBOX_CONFIG_FEATURE_LESS_FLAGS=y
CONFIG_BUSYBOX_CONFIG_FEATURE_LESS_REGEXP=y
CONFIG_BUSYBOX_CONFIG_FEATURE_LESS_WINCH=y
# Add-on programs
CONFIG_PACKAGE_ccrypt=y
CONFIG_PACKAGE_curl=y
CONFIG_LIBCURL_OPENSSL=y
CONFIG_PACKAGE_diffutils=y
CONFIG_DROPBEAR_ECC=y
CONFIG_PACKAGE_htop=y
CONFIG_PACKAGE_irqbalance=y
CONFIG_PACKAGE_mtr-nojson=y
CONFIG_PACKAGE_nano-full=y
CONFIG_PACKAGE_patch=y
CONFIG_PACKAGE_tcpdump-mini=y
CONFIG_PACKAGE_tree=y
CONFIG_PACKAGE_wget-ssl=y
# USB device mount & file systems support
CONFIG_PACKAGE_block-mount=y
CONFIG_PACKAGE_kmod-usb-storage=y
CONFIG_PACKAGE_kmod-fs-cifs=y
CONFIG_PACKAGE_kmod-fs-exfat=y
CONFIG_PACKAGE_libblkid=y
CONFIG_PACKAGE_kmod-fs-ext4=y
CONFIG_PACKAGE_kmod-fs-hfsplus=y
CONFIG_PACKAGE_kmod-fs-msdos=y
CONFIG_PACKAGE_kmod-fs-ntfs3=y
CONFIG_PACKAGE_kmod-nls-cp1250=y
CONFIG_PACKAGE_kmod-nls-cp437=y
CONFIG_PACKAGE_kmod-nls-cp850=y
CONFIG_PACKAGE_kmod-nls-iso8859-1=y
CONFIG_PACKAGE_kmod-nls-iso8859-15=y
CONFIG_PACKAGE_kmod-nls-utf8=y
# IPv6 support
CONFIG_PACKAGE_6in4=y
CONFIG_PACKAGE_6to4=y
CONFIG_PACKAGE_6rd=y
# WLAN/WPS support
CONFIG_PACKAGE_hostapd-utils=y
#CONFIG_WPA_MSG_MIN_PRIORITY=2
CONFIG_PACKAGE_wpad-openssl=y
# CONFIG_PACKAGE_wpad-basic-mbedtls is not set
# CONFIG_PACKAGE_libustream-mbedtls is not set
# SSL certificates
CONFIG_PACKAGE_ca-certificates=y
# Luci (SSL from OpenSSL)
CONFIG_PACKAGE_luci-ssl-openssl=y
CONFIG_PACKAGE_luci-app-commands=y
CONFIG_PACKAGE_luci-app-ddns=y
CONFIG_PACKAGE_luci-app-opkg=y
CONFIG_PACKAGE_luci-app-sqm=y
CONFIG_PACKAGE_luci-app-uhttpd=y
CONFIG_PACKAGE_luci-app-upnp=y
# CONFIG_LUCI_JSMIN is not set
# Luci statistics
CONFIG_PACKAGE_luci-app-statistics=y
CONFIG_PACKAGE_collectd-mod-conntrack=y
CONFIG_PACKAGE_collectd-mod-cpufreq=y
CONFIG_PACKAGE_collectd-mod-dhcpleases=y
CONFIG_PACKAGE_collectd-mod-entropy=y
CONFIG_PACKAGE_collectd-mod-ping=y
CONFIG_PACKAGE_collectd-mod-sqm=y
CONFIG_PACKAGE_collectd-mod-thermal=y
CONFIG_PACKAGE_collectd-mod-uptime=y
# Build openwrt-2020 theme, default is still bootstrap
CONFIG_PACKAGE_luci-theme-openwrt-2020=y
# kernel support for tunnels, VPNs
CONFIG_PACKAGE_kmod-tun=y
# wireguard and unetd (new wg-based mesh VPN)
CONFIG_PACKAGE_luci-proto-wireguard=y
CONFIG_PACKAGE_luci-proto-unet=y
# PPTP support
CONFIG_PACKAGE_luci-proto-ppp=y
CONFIG_PACKAGE_ppp-mod-pptp=y
# iptables add-on ipsec
CONFIG_PACKAGE_iptables-mod-ipsec=y
# Support for IETF BCP38
CONFIG_PACKAGE_luci-app-bcp38=y
# Adblock package with Luci support, initially disabled
CONFIG_PACKAGE_luci-app-adblock=y
# BanIP package with Luci support, initially disabled
CONFIG_PACKAGE_luci-app-banip=y
# nlbwmon app
CONFIG_PACKAGE_luci-app-nlbwmon=y
# chaoskey TRNG USB dongle
####CONFIG_PACKAGE_kmod-chaoskey=y
## Build and include qosify, if the LLVM toolchain has been downloaded and
## extracted to the buildroot before the build config is started.
## The file can be downloaded from buildbot snapshot target downloads.
## https://downloads.openwrt.org/snapshots/targets/ipq806x/generic/llvm-bpf-15.0.7.Linux-x86_64.tar.xz
##
CONFIG_USE_LLVM_PREBUILT=y
CONFIG_PACKAGE_qosify=y
CONFIG_PACKAGE_kmod-sched-bpf=y
# NFT support for iptables
CONFIG_PACKAGE_iptables-nft=y
CONFIG_PACKAGE_ip6tables-nft=y
# ipset and kernel module
CONFIG_PACKAGE_ipset=y
# sftp server lib for newest scp in Ubuntu
CONFIG_PACKAGE_openssh-sftp-server=y