"Harald Nordgren via GitGitGadget" [off-list ref] writes:

 t/helper/test-%$X: t/helper/test-%.o GIT-LDFLAGS $(GITLIBS)
-	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) $(filter %.a,$^) $(LIBS)
+	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) $(LIBS)

I think the reason why the pattern to use only the .o files among
the prerequisites and then use only the .a files among the same
prerequisites (both filters $^) is used here is to make sure that the
linker sees object files first before library archives, so that by
the time its left-to-right scan sees the first library archive, all
the missing symbols in the object files are known.  The above change
depends on LIBS being a strict superset of all the library archive
files ($GITLIBS in the current code, but that can be updated in the
future) listed as prerequisites for the rule, but there is nothing to
guarantee that, so it looks brittle.

Exact same comment applies to the other two rules touched by this patch.