posix

Backport changes to properly hide non-interface functions #608

Job	Run time
build (ubuntu-latest, i686, 0, 2014, manylinux)	7m 16s
build (macos-latest, arm64, 0, macosx)	13m 7s
build (macos-14, x86_64, 0, macosx)	15m 29s
build (macos-14, x86_64, 1, macosx)	11m 46s
build (ubuntu-latest, x86_64, 0, 2014, manylinux)	8m 14s
build (ubuntu-24.04-arm, aarch64, 0, 2014, manylinux)	6m 52s
build (ubuntu-latest, x86_64, 1, _1_2, musllinux)	11m 1s
build (macos-latest, arm64, 1, macosx)	15m 8s
build (ubuntu-latest, x86_64, 0, _1_2, musllinux)	11m 28s
build (ubuntu-24.04-arm, aarch64, 1, _1_2, musllinux)	8m 26s
build (ubuntu-24.04-arm, aarch64, 0, _1_2, musllinux)	9m 13s
build (ubuntu-latest, x86_64, 1, 2014, manylinux)	8m 20s
build (ubuntu-24.04-arm, aarch64, 1, 2014, manylinux)	8m 31s
	2h 14m 51s

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