Good read: LibreSSL: More Than 30 Days Later
I loved this bit:
I could spend an hour explaining why supporting obsolete broken systems is detrimental, but if I told you all the things I have learned about VMS, it would probably violate your human rights. Instead, I think one example will suffice.
In theory, this looks like we’re going to use the good code on a posix system. But there’s just one problem. The code is testing for FIONBIO, which is only defined if you include the right header. If you forget to include the right header, the compiler falls back to the workaround. The mere existence of workarounds means they can be picked up accidentally, and you’ll never know.