...at least in com_GCC_class.mk (com_MSC_class.mk will be addressed in a follow-
up commit), after the recent loplugin:includeform clean-up.

Two static libraries built from external sources needed adjustment, two
compilerplugin tests needed adjustment (which wasn't found by
loplugin:includeform, by design), and one more adjustment in
sal/textenc/generate/.

Change-Id: Idad5ae355a02ae130369a9a45b5f5925ab48ffef
Reviewed-on: https://gerrit.libreoffice.org/44174Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>