Maybe use $? for archive updates?

[dbosk]

$?: The names of all the prerequisites that are newer than the target, with spaces between them. For prerequisites which are archive members, only the named member is used (see Archives).

This way we only update the out-of-date archive members.

[dbosk]

It doesn't seem to make sense for archive members. There is an example in the documentation:

lib: foo.o bar.o lose.o win.o
        ar r lib $?

which doesn't use the archive member notation.