[PROJ] Updating our C++ requirement to C++17 for PROJ 9.6

[Howard Butler]

> On Jan 2, 2025, at 5:54 PM, Even Rouault via PROJ <proj at lists.osgeo.org> wrote:
> 
> Hi,
> 
> Happy New Year!
> 
> I propose we update our build requirement from C++11 to C++17. This should hopefully be unnoticed by anyone using a not too antiquated build chain.
> 
> Initial trigger for this move is explained in https://github.com/OSGeo/PROJ/pull/4366. All our existing CI configurations already satisfy the C++17 requirement (and one of them was already testing C++20 compatibility)
> 
> I don't anticipate much use of new capabilities for now except perhaps replacing our internal::make_unique<> by C++14 std::make_unique<>
> 
> C++17 has been a build requirement for GDAL since one year and nobody complained. Cf https://gdal.org/en/stable/development/rfc/rfc98_build_requirements_gdal_3_9.html for an analysis of the impacts.
> 
> This also satisfies https://proj.org/en/stable/community/rfc/rfc-3.html which mentions "Keeping a policy of always lagging behind be two iterations of the standard is thought to be the best comprise between the two concerns", given that C++20 and C++23 are out.


Is this a PSC motion? +1 :)

Howard