scalar: make the build rule more generic

We already define via `SCALAR_OBJS` which object files are specific to
Scalar. Let's use them in the Makefile rule that builds the `scalar`
executable.

This is needed for the next commit, where we add a JSON parser in
preparation for supporting Azure Repos.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Makefile

@@ -2741,7 +2741,7 @@ $(REMOTE_CURL_PRIMARY): remote-curl.o http.o http-walker.o GIT-LDFLAGS $(GITLIBS
 	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) \
 		$(CURL_LIBCURL) $(EXPAT_LIBEXPAT) $(LIBS)
 
-scalar$X: scalar.o GIT-LDFLAGS $(GITLIBS)
+scalar$X: $(SCALAR_OBJS) GIT-LDFLAGS $(GITLIBS)
 	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) \
 		$(filter %.o,$^) $(LIBS)