I wrote:
> * Both clang and gcc seem to be happy with the same spelling of the
> function attribute, which is fortunate. However, I seriously doubt
> that bare "#ifdef __GNUC__" is going to be good enough. At the very
> least there's going to need to be a compiler version test in there,
> and we might end up needing to get the configure script involved.
After digging in gcc's release history, it seems they invented
"-fsanitize=alignment" in GCC 5, so we can make this work for gcc
by writing
#if __GNUC__ >= 5
(the likely() macro already uses a similar approach). Can't say
if that's close enough for clang too.
regards, tom lane