...in anticipation of building with clang-cl.exe on Windows

Change-Id: I1d723c9d3b5ca8a2bc6b27ef0189a7b053581398
Reviewed-on: https://gerrit.libreoffice.org/19928Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>