https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108531
--- Comment #5 from Keith Thompson <Keith.S.Thompson at gmail dot com> --- FYI, I've sent an email to the C standard editors (the addresses at the top of the N3054 draft) suggesting that imaginary number support should be optional even if __STDC_IEC_559_COMPLEX__ and __STDC_IEC_60559_COMPLEX__ are defined. It's probably too late to make such a change in C23. (__STDC_IEC_60559_COMPLEX__ is replacing __STDC_IEC_559_COMPLEX__, which is obsolescent.)
