C and C++ compiler extensions disabled in extra-cmake-modules

[Friedrich W. H. Kossebau]

Am Montag, 28. Juni 2021, 01:05:37 CEST schrieb Albert Astals Cid:
> With
> https://invent.kde.org/frameworks/extra-cmake-modules/-/merge_requests/145
> we have disabled the C and C++ specific compiler extensions.
> 
> This has already let to some code failing to build that was using C
> extensions, and has been fixed by simply requiring a more recent C
> https://invent.kde.org/frameworks/kguiaddons/-/merge_requests/23
> https://invent.kde.org/frameworks/bluez-qt/-/merge_requests/10
>   https://invent.kde.org/frameworks/kwayland/-/merge_requests/34

As this breaks the build of existing released software and thus is not 
backward-compatible (e.g. some of KDE Gear 21.04 will not blend with ECM 
5.84), that new setting needs to be rather actively triggered.

A mechanism used before is requiring a certain minimum version of ECM to 
activate the new setting.

Proposed in
https://invent.kde.org/frameworks/extra-cmake-modules/-/merge_requests/148

Cheers
Friedrich