Makefile: avoid libcurl when building git

We don't need support for fetching/pushing in libgit.a, hence we don't need
to link with libcurl.

Noticed-by: Robin Redeker <elmex@ta-sa.org>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

Makefile

@@ -128,8 +128,8 @@ cgit.o: VERSION
 -include $(OBJECTS:.o=.d)
 
 libgit:
-	$(QUIET_SUBDIR0)git $(QUIET_SUBDIR1) libgit.a
-	$(QUIET_SUBDIR0)git $(QUIET_SUBDIR1) xdiff/lib.a
+	$(QUIET_SUBDIR0)git $(QUIET_SUBDIR1) NO_CURL=1 libgit.a
+	$(QUIET_SUBDIR0)git $(QUIET_SUBDIR1) NO_CURL=1 xdiff/lib.a
 
 test: all
 	$(QUIET_SUBDIR0)tests $(QUIET_SUBDIR1) all