Configurations/unix-Makefile.tmpl: overhaul assembler make rules.

So far assembly modules were built as .pl->.S->.s followed by .s->.o.
This posed a problem in build_all_generated rule if it was executed
on another computer. So we change rule sequence to .pl->.S and then
.S->.s->.o.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5573)