Also create a Clang compiler plugin to detect such cases.

Change-Id: I61ad1a1d6b1c017eeb51f226d2dde0e9bb7f1752
Reviewed-on: https://gerrit.libreoffice.org/4001Tested-by: LibreOffice gerrit bot <gerrit@libreoffice.org>
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>