Numerous build regressions

[Friedrich W. H. Kossebau]

Am Sonntag, 25. April 2021, 09:56:17 CEST schrieb Ben Cooksley:
> These failures appear to be due to changes to the export header templates
> in extra-cmake-modules, and some SSL related functions in KIO.

Looking into the export header related one. Seems that bluez-qt includes the 
export header also from C code, and the C preprocessor of clang (?) on FreeBSD 
seems to handle a directive like
    #if defined(__has_cpp_attribute) && __has_cpp_attribute(deprecated)
not as one like myself would expect it, stopping evaluation before the && ?

08:25:02  /usr/home/jenkins/workspace/Administration/Dependency Build 
Extragear kf5-qt5 FreeBSDQt5.15/bluez-qt/build/src/bluezqt_export.h:42:37: 
error: function-like macro '__has_cpp_attribute' is not defined
08:25:02  #if defined(__has_cpp_attribute) && __has_cpp_attribute(deprecated)

Guess that needs some #ifdef __cplusplus protection of some kind. Anyone 
experience with that, while I am learning while writing such code now?

Cheers
Friedrich