Configurations/unix-Makefile.tmpl: fix inconsistencies with resource files

.res files weren't treated consistently.  They weren't included at all
in the build of a shared library, and were named inconsistently; .res
sometimes, and .res.o otherwise.  Now we standardise it to .res.o,
which is the recommended way with GNU tools.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5730)