tdf#42949 Add filter file to unoidl/

Seems I forgot about this in commit
7f6a5b43

Change-Id: Ic575292b99836374f179cbc1dbe182858415b63f
Reviewed-on: https://gerrit.libreoffice.org/71306
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

unoidl/IwyuFilter_unoidl.yaml

+---
+assumeFilename: unoidl/source/unoidl.cxx
+blacklist:
+    unoidl/source/unoidl-write.cxx:
+    # Avoid loplugin:oslendian error
+    - osl/endian.h