Among others, this avoids having special variables like
PROGRAMS_NO_INST.  Instead, we can have something like this:

    PROGRAMS{noinst}=foo bar

Configure itself is entirely agnostic to these attributes, they are
simply passed to the build file templates, to be used as they see fit.

Attributes can also have values, for example:

    SCRIPTS{linkname=foo}=foo.pl

This could help indicate to build file templates that care that the
perl script 'foo.pl' should also exist with the name 'foo', preferably
as a symbolic link.

Fixes #7568
Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7581)