add missing stddef includes #1352

Job	Run time
build_debian_buster	3m 10s
build_debian_bullseye	3m 17s
build_android	12m 6s
build_debian_bookworm	3m 56s
build_debian_sid	3m 39s
build_macos_arm	2m 28s
build_raspios_bullseye_armhf	8m 57s
build_macos_intel	4m 37s
build_ubuntu_focal	3m 37s
build_ubuntu_jammy	3m 22s
build_ubuntu_mantic	3m 19s
build_windows	13m 40s
build_ubuntu_noble	3m 57s
check_formatting	13s
check_spelling	14s
create_full_archive	17s
update_nightly_release	6s
	1h 10m 55s

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