[PROJ] 9.6.0 sharp embed compiler test on gcc7

[Greg Troxel]

Even Rouault <even.rouault at spatialys.com> writes:

> A fix for that has been merged in the 9.6 branch (post 9.6.0, for
> 9.6.1) per https://github.com/OSGeo/PROJ/pull/4463

Thanks, am cherry-picking that into pkgsrc.  With gcc 10 the build diff
is that the following lines vanish, changing a failing embed test into
"not trying because gcc10 < gcc15".

  -- Performing Test _TEST_SHARP_EMBED
  -- Performing Test _TEST_SHARP_EMBED - Failed

With NetBSD 9 and gcc 7, it also successfully built.
Tests pass except for spilhaus, which I realize is new and I'll look
into that - surely not relatd to C23/embed.

>> I also don't understand how C23 is handled if sharp embedding is turned
>> on.  It would seem one has to end up passing --std for it, because a
>> compiler that can compile C23 does not necessarily default to it.
> Cf
> https://github.com/OSGeo/PROJ/blob/41139273222d1a5937ff6abcf16350f6ed7db773/src/lib_proj.cmake#L429
> that selectively enables C23 for targets that need it when
> IS_SHARP_EMBED_AVAILABLE_RES is set.

Ah, did not guess that from the original cmake code, but makes sense.

>> Does this work for others on compilers that don't support C23?
> If they are not too old yes.

It worked with 7 which is my current take on "oldest gcc that is not
unreasonably ancient" but idk what's up with older RHEL and older ubuntu
that people run, these days.