...since de030cd7a2 "gbuild: Remove MSVC 2013
legacy code", so no longer treat it as such in compilerplugins. (Which caused a
few loplugin:includeform and loplugin:nullptr warnings.)
Change-Id: I99b42e76992e31aff56b417c05738d4d29e3faf9
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/112575
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>