bug#75451: scratch/igc: Enable CHECK_STRUCTS

[Stefan Kangas <stefankangas@gmail.com>]

Pip Cet <pipcet@protonmail.com> writes:

> This isn't strictly about the scratch/igc branch, but I personally think
> struct hashes should be checked in all builds, mismatches should be
> downgraded to #warnings, and --enable-checking=all could include
> -Werror=cpp.  (So the warnings would still abort a build with
> --enable-checking=all, but they'd *also* show up in regular builds.)

Sounds good to me.

> Also, we should include them in the nativecomp ABI hash, as nativecomp
> relies on struct layout and the tagging scheme in nontrivial ways
> (most-positive-fixnum, for example, is treated as a compile-time
> constant by comp.el, but I'm not sure all changes to it would
> automatically affect the comp abi hash).

I'm copying in Andrea for this part.

> Changes required might include:
>
> * autodetection of gawk vs awk (I think this simply means using $(AWK)
>   rather than "awk" in src/Makefile.in; this is important on some
>   machines which provide a very different "awk")

Using $(AWK) instead of raw "awk" makes sense, because why not.

But which awk implementations are you concerned about more specifically?
I would expect us to just use POSIX awk, without any gawk extensions.
For example, I have had no issues building on Debian (using mawk by
default) or macOS (with the BSD awk that descends from nawk, IIUC).

> * igc.o and comp.o  should depend explicitly on dmpstruct.h (this is
>   important for re-builds; in theory, the current scratch/igc branch is
>   broken for highly parallel builds because dmpstruct.h might be
>   generated after igc.o, but that is not important).

Sounds good also.

> * a hash-of-hashes for nativecomp
>
> Proposed partial patch:

(I didn't look at the patch yet, though the above sounds like it might
come out to more than one patch.)