Missing __libc_single_threaded@GLIBC_2.32

[kkofler]

I have a library using this (the same where I also have issue #11). (This is not as urgent as #11 for me because right now I am trying to make it work on glibc 2.34, which has this function, but I tried setting an older glibc target and got this as an additional error.)

See: https://www.gnu.org/software/libc/manual/html_node/Single_002dThreaded.html – the simplest (poor, but valid) implementation is to just map this to a constant char which is always 0.