stage2 CBE: Improve support for unions and error sets
This includes various fixes/improvements to the C backend to improve
error/union support. It also fixes up our handling of decls, where some
decls were not correctly marked alive.
a9a91a5d49Cody Tapscott committed on 3/23/2022, 8:29:38 PM· committed by Andrew Kelleyparent2f9264d