fdo#46847 fix build of so_activex.rc

Use \ instead of / in path, but more importantly,
use relative path, because '-' in path caused build error.
Path was truncated right before the '-'. We could have put it
between quotes, but then the SO_ACTIVEX_TLB_DIR define would not
be substituted, so instead of hacking of the rc, I chose this
solution.

e

extensions/WinResTarget_activex.mk

@@ -41,7 +41,7 @@ $(eval $(call gb_WinResTarget_add_file,activex_res,extensions/source/activex/so_
 
 $(eval $(call gb_WinResTarget_set_defs,activex_res,\
 	$$(DEFS) \
-	-DSO_ACTIVEX_TLB_DIR=$(call gb_Helper_convert_native,$(WORKDIR)/CustomTarget/extensions/source/activex/idl) \
+	-DSO_ACTIVEX_TLB_DIR=$(subst /,\\,$(subst $(call gb_Helper_convert_native,$(SRCDIR)),../../..,$(call gb_Helper_convert_native,$(WORKDIR)/CustomTarget/extensions/source/activex/idl))) \
 ))
 
 # I suppose this dep is not really necessary, because it should always