kconfig: fix qconf (make xconfig) linking

qconf is written in C++, so use HOSTCXX instead of HOSTCC, and pass the
correct flags.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/config/Makefile

@@ -26,7 +26,7 @@ $(host-cmulti): %: $(host-cobjs) $(host-cshlib)
 	$(HOSTCC) $(HOST_EXTRACFLAGS) $(HOSTCFLAGS) $(HOSTCFLAGS_$@) $($@-objs) $(HOST_LOADLIBES) -o $@
 
 $(host-cxxmulti): %: $(host-cxxobjs) $(host-cobjs) $(host-cshlib)
-	$(HOSTCC) $(HOST_EXTRACFLAGS) $(HOSTCFLAGS) $(HOSTCFLAGS_$@) $($@-objs) $($@-cxxobjs) $(HOSTLOADLIBES_$@) -o $@
+	$(HOSTCXX) $(HOST_EXTRACFLAGS) $(HOSTCFLAGS) $(HOSTCXXFLAGS_$@) $($@-objs) $($@-cxxobjs) $(HOSTLOADLIBES_$@) -o $@
 
 $(host-cobjs): %.o: %.c
 	$(HOSTCC) $(HOST_EXTRACFLAGS) $(HOSTCFLAGS) $(HOSTCFLAGS_$@) -c $< -o $@