Prevent -Werror,-Wunknown-warning-option when building compilerplugins

...with --enable-werror (seen it fail with a local build against a locally
built Clang 5.0.2).

(bin/gen-boost-headers faces a similar dilemma with Clang needing to silence
-Wunknown-warning-option and GCC failing upon the silencing incantation.  There,
we were able to hack around that with a preceding

#pragma GCC diagnostic ignored "-Wpragmas"

Here, the easiest approach appears to be a new COMPILER_PLUGINS_COM_IS_CLANG
analoguous to the existing COM_IS_CLANG.)

Change-Id: I9036261fdd238c8a020a1d88b4e75fd444f9e030
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/88725
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

0 files changed, 0 insertions, 0 deletions