...after <https://gerrit.libreoffice.org/63951> "Bump (Linux) GCC baseline to
7.0.0".  (In some cases, those checks now need to check for __clang__, which was
implicitly covered in the past by Clang consistently reporting to be
GCC 4.2.1.)

Change-Id: I860fef8c4ca41c22a7541f0fb2d34b37d1d69bed
Reviewed-on: https://gerrit.libreoffice.org/63952
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>