compilerplugins: fix referencecasting for clang 7.0.1

The error was:

error: 'error' diagnostics seen but not expected:
File /libreoffice/master-clang/compilerplugins/clang/test/referencecasting.cxx Line 113: unnecessary get() call [loplugin:referencecasting]
1 error generated.

I.e. it seems clang7 has the same problem as clang5 that it emits
multiple diagnostics for that problematic code line. Adapt the ifdef
accordingly.

Change-Id: I232ff9a158663e2cb3030e51f655249ff315361e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/111196
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>

0 files changed, 0 insertions, 0 deletions