deskutils/kdepim-runtime: fix build with clang 21
With clang 21 deskutils/kdepim-runtime fails to build, with errors
similar to:
ld: error: undefined symbol: KPIM::Maildir::Maildir(QString const&, bool) >>> referenced by configwidget.cpp >>> CMakeFiles/mixedmaildirconfig.dir/configwidget.cpp.o:(ConfigWidget::checkPath()) >>> referenced by configwidget.cpp >>> CMakeFiles/mixedmaildirconfig.dir/configwidget.cpp.o:(ConfigWidget::checkPath()) ld: error: undefined symbol: KPIM::Maildir::isValid(bool) const >>> referenced by configwidget.cpp >>> CMakeFiles/mixedmaildirconfig.dir/configwidget.cpp.o:(ConfigWidget::checkPath()) >>> referenced by configwidget.cpp >>> CMakeFiles/mixedmaildirconfig.dir/configwidget.cpp.o:(ConfigWidget::checkPath())
This is because various CMake configure checks fail, due to the port
Makefile adding -Wno-error=enum-constexpr-conversion, which is no longer
supported by clang >= 21.
PR: 293955
Approved by: makc (maintainer)
MFH: 2026Q1
(cherry picked from commit 441cd2b7a4f5b81f25ac9109b30c646265e7f7fb)