Should note that glibc now supports c11 threads. AFAIK there was some problem with their initial specification that caused them to want not to implement them,

Should note that glibc now supports c11 threads. AFAIK there was some problem with their initial specification that caused them to want not to implement them, and c18 amended that so they're now comfortable supporting them. Also note that openrisc has been mostly superceded by risc-v, which afaik glibc and musl both support; don't know about the other libcs.