Missing CppunitTest dependencies on new macOS/Windows vclplug backends

...after 1698debe "Implement Windows VCL backend
as plugin" and 3af4e1a0 "Implement MacOSX VCL
backend as plugin".  (On these platforms, the tests apparently call into the
respective vclplug backend code regardless of whether the test is "headless" or
not.)

Change-Id: I6d93eacd9f94047add94ba3e866e6be1eb35c879
Reviewed-on: https://gerrit.libreoffice.org/61376Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

solenv/gbuild/CppunitTest.mk

@@ -236,6 +236,10 @@ $(call gb_CppunitTest_get_target,$(1)) : $(if $(filter $(2),$(true)),, \
         $(if $(ENABLE_KDE4),$(call gb_Library_get_target,vclplug_kde4)) \
         $(if $(ENABLE_QT5),$(call gb_Library_get_target,vclplug_qt5)) \
 	 )
+else ifeq ($(OS),MACOSX)
+$(call gb_CppunitTest_get_target,$(1)): $(call gb_Library_get_target,vclplug_osx)
+else ifeq ($(OS),WNT)
+$(call gb_CppunitTest_get_target,$(1)): $(call gb_Library_get_target,vclplug_win)
 endif
 
 endef