It's used at build time in 7 crates (6 directly).

Depender (with downloads and own rev deps) urcu2-src version
6 urcu2-sys build ^0.1.5
1 urcu2-qsbr-sys build ^0.1.5
1 urcu2-bp-sys build ^0.1.5
1 urcu2-mb-sys build ^0.1.5
1 urcu2-memb-sys build ^0.1.5
1 urcu2-cds-sys build ^0.1.5