gbuild: allow to depend on headers of a library

... even if we do not link with it. This was previously solved by
delivering the headers to solver and depending on the Package.

Change-Id: Id1b53b88d54226cb3ce02f5f2424632596fa069a

solenv/gbuild/Library.mk

@@ -260,6 +260,7 @@ $(eval $(foreach method,\
 	use_package \
 	use_packages \
 	use_unpacked \
+	use_headers \
 	add_package_headers \
 	add_sdi_headers \
 	set_precompiled_header \

solenv/gbuild/LinkTarget.mk

@@ -1371,6 +1371,17 @@ $(call gb_LinkTarget_get_external_headers_target,$(1)) :| $(call gb_ExternalProj
 
 endef
 
+# Use headers provided by another link target.
+#
+# This function should only be needed to enforce correct build ordering,
+# if the link target does not use the other link target.
+#
+# gb_LinkTarget_use_headers linktarget other-linktarget(s)
+define gb_LinkTarget_use_headers
+$(call gb_LinkTarget_get_external_headers_target,$(1)) :\
+    $(foreach linktarget,$(2),$(call gb_LinkTarget_get_headers_target,$(linktarget)))
+
+endef
 
 # this forwards to functions that must be defined in RepositoryExternal.mk.
 # $(eval $(call gb_LinkTarget_use_external,library,external))

svx/Library_svxcore.mk

@@ -378,6 +378,10 @@ $(eval $(call gb_Library_add_exception_objects,svxcore,\
 
 ifneq (,$(filter DBCONNECTIVITY,$(BUILD_TYPE)))
 
+$(eval $(call gb_Library_use_headers,svxcore,\
+	dbtools \
+))
+
 $(eval $(call gb_Library_add_exception_objects,svxcore,\
     svx/source/fmcomp/dbaexchange \
     svx/source/fmcomp/fmgridcl \