Because this also includes handling all sorts of non-object files when
linking a program, shared library or DSO, this also includes allowing
general recognition of files such as .res files (compiled from .rc
files), or .def / .map / .opt files (for export and possibly
versioning of public symbols only).

This does mean that there's a tangible change for all build file
templates: they must now recognise and handle the `.o` extension,
which is used internally to recognise object files internally.  This
extension was removed by common.tmpl before this change, but would
mean that the platform specific templates wouldn't know if "foo.map"
was originally "foo.map.o" (i.e. an object file in its own right) or
"foo.map" (an export definition file that should be treated as such,
not as an object file).

For the sake of simplifying things, we also modify util/mkdef.pl to
produce .def (Windows) and .opt (VMS) files that don't need additional
hackery.
Reviewed-by: NAndy Polyakov <appro@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4840)