os: freeze signals constant #1572

Job	Run time
Build slim tarball	1m 23s
x86_64-darwin: with shared libraries	3h 55m 36s
x86_64-linux: with shared libraries	2h 21m 33s
aarch64-linux: with shared libraries	2h 10m 45s
aarch64-darwin: with shared libraries	2h 2m 2s
	10h 31m 19s

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