odroidxu4: fix u-boot build on trixie (GCC 14 implicit-decl errors)

CI "Build All Artifacts" failed uboot-odroidxu4-current on the trixie host:

  drivers/mmc/mmc_boot.c:120:13: error: implicit declaration of function
  'mmc_rst_n_func_status' [-Wimplicit-function-declaration]

GCC 14 promotes -Wimplicit-function-declaration (plus -Wimplicit-int and
-Wincompatible-pointer-types) from warning to hard error by default. This
2017-era hardkernel u-boot (odroidxu4-v2017.05) predates that and trips on it;
it built fine on noble/GCC 13. The SWIG/pylibfdt break is unrelated here and
already handled by the board's fix_build_for_recent_host-side_libfdt +
fix-compilation-on-noble (distutils->setuptools) patches.

Add a post_config_uboot_target hook that appends the three -Wno-error= flags to
uboot_cflags_array (same mechanism as rockchip-rv1106's GCC-downgrade hook). The
missing prototypes are cosmetic - the functions are defined at link time - so
downgrading to warnings is safe and keeps the known-good hardkernel boot chain.

Signed-off-by: Igor Pecovnik <igor@armbian.com>

Author: igorpecovnik

config/sources/families/odroidxu4.conf

@@ -52,6 +52,20 @@ function custom_kernel_config__hack_odroidxu4_firmware() {
 	fi
 }
 
+# GCC 14 on the trixie host promotes -Wimplicit-function-declaration (and
+# -Wimplicit-int / -Wincompatible-pointer-types) from warning to hard error,
+# which this 2017-era hardkernel u-boot trips on (e.g. mmc_rst_n_func_status in
+# drivers/mmc/mmc_boot.c). Downgrade them back to warnings so it builds again;
+# the symbols are defined at link time, only their prototypes are missing.
+function post_config_uboot_target__odroidxu4_downgrade_gcc14_errors() {
+	uboot_cflags_array+=(
+		"-Wno-error=implicit-function-declaration"
+		"-Wno-error=implicit-int"
+		"-Wno-error=incompatible-pointer-types"
+	)
+	return 0
+}
+
 setup_write_uboot_platform() {
 	# this will update u-boot on the device rootfs is located on
 	# in case it's a mmc device, otherwise DEVICE will not be changed