see <https://github.com/llvm/llvm-project/commit/
76b9027f352a83c13c98820724071c5e3bea6232> "[c++20] Add support for
explicit(bool), as described in P0892R2."

Change-Id: Ia8a6902a64ab3377328fd5e3ed57246d214176f2
Reviewed-on: https://gerrit.libreoffice.org/72335
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>