Turns out SdiTarget needs the extended SOLARINC after all

After fbfe55e5 "There appears to be no need for
-I. in SOLARINC", on Windows, e.g. workdir/Dep/SdiTarget/basctl/sdi/basslots.d
now contains basslots.sdi without a path, because the call to
osl::File::searchFileURL in SvIdlParser::ReadInclude (idl/source/prj/parser.cxx)
is done with rBase.GetPath() no longer containing the basctl/sdi/ source dir, so
searchFileURL silently returns "basslots.sdi" unmodified.  (The non-Windows
implementation in sal/osl/unx/file_url.cxx appears to also check CWD, so doesn't
suffer from this regression.)

Change-Id: I51802192cfe112f810b193a77d14787d965c2761
Reviewed-on: https://gerrit.libreoffice.org/45323Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

solenv/gbuild/SdiTarget.mk

@@ -63,7 +63,7 @@ $(call gb_SdiTarget_get_clean_target,%) :
 			$(call gb_SdiTarget_get_target,$*))
 
 define gb_SdiTarget_SdiTarget
-$(call gb_SdiTarget_get_target,$(1)) : INCLUDE := $(SOLARINC)
+$(call gb_SdiTarget_get_target,$(1)) : INCLUDE := $(SOLARINC) -I$$(dir $(SRCDIR)/$(1))
 $(call gb_SdiTarget_get_target,$(1)) : EXPORTS := $(SRCDIR)/$(2).sdi
 ifeq ($(gb_FULLDEPS),$(true))
 -include $(call gb_SdiTarget_get_dep_target,$(1))