gcc-15-160000.2.2

- Bump GCC version to 15, leave -build flavor at 13.

- Check is_opensuse for whether plugins are enabled.

- Ensure every -build package conflicts and provides the non-build
  counterpart (related to boo#1230628)

- Make gcc-build-fortran provide and conflict gcc-fortran.

- Add libquadmath-devel package for GCC 14.
- Bump GCC version to 14, leave -build flavor at 13.

- Add conflicts where -build variants provide the non-build variant.

- Add gcc, gcc-c++ and libstdc++-devel Provides to the -build flavor
  of those packages.  Should fix build of boost in ALP.

- Add gcc-build flavor for building ALP packages, but disabled for
  openSUSE.

- Support building suffixed packages, but only allow installing one
  variant at the same time.
- Remove obsolete obsoletes.

- Switch gcc to default 13.