temporary hack: soffice.bin should be type of GUI app, not CUI app fdo#42914

It is puzzling that Executable_soffice.bin.mk contains the line
$(eval $(call gb_Executable_set_targettype_gui,$(sofficebin),YES))
yet, in the build log we see -SUBSYSTEM:CONSOLE among the linker flags.
I added -SUBSYSTEM:WINDOWS flag exlicitely, and it comes later so it
prevails. I guess MinGW will be still affected. It really should be
fixed correctly by a gbuild expert.

desktop/Executable_soffice.bin.mk

@@ -58,6 +58,7 @@ ifeq ($(COM),MSC)
 
 $(eval $(call gb_Executable_add_ldflags,$(sofficebin),\
     /STACK:10000000 \
+    /SUBSYSTEM:WINDOWS \
 ))
 
 endif