Do not filter out libsax from installation even if it's merged

expwrap links against sax and can't link against libmerged because
it is needed to build libmerged :-/ (saxparser in i18npool)

Change-Id: Ie4dca11e8e1bb16a2506cf7cdb7d69b804d98cc0
Reviewed-on: https://gerrit.libreoffice.org/15447Tested-by: Jenkins <ci@libreoffice.org>
Tested-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>

solenv/gbuild/Helper.mk

@@ -191,7 +191,7 @@ $$(eval $$(call gb_Output_error,$(1) is not a valid group for installed librarie
 endif
 $(call gb_Helper__register_libraries,$(1),$(3))
 
-gb_Library_MODULE_$(2) += $(filter-out $(gb_MERGEDLIBS),$(3))
+gb_Library_MODULE_$(2) += $(filter-out $(filter-out sax,$(gb_MERGEDLIBS)),$(3))
 
 $(if $(filter UNOVERLIBS RTVERLIBS,$(1)),\
 	gb_SdkLinkLibrary_MODULE_sdk += $(3))