The remainder of the patch series proposed by upstream [2] for the locking
synchronization issue [1].

[1] https://www.openwall.com/lists/musl/2020/05/22/3
[2] https://www.openwall.com/lists/musl/2020/05/22/10



Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>