bug#36929: 27.0.50; Build on master broken

[Paul Eggert]

> Should we maybe define CHECK_STRUCTS unconditionally to prevent issues
> like this?

Let's not, because CHECK_STRUCTS is more trouble than it's worth when doing 
serious development. See commit 9994bf17cf532f2e1d4310341da7180342202191 and 
related discussion.

If you run into this problem again, feel free to do what Eli did and commit a 
change to the hash to get your --enable-checking=structs build to work again. I 
don't bother because --enable-checking=structs is a waste of time for me, and I 
recommend against it.