rtld: Add ${TOKEN} aliases to $TOKEN

it seems that glibc supports them, and such spelling is mentioned in the
ld.bfd manual. Idea seems to auto-correct some quoting/makefile sytnax
errors on linker command line.

Reviewed by: emaste, markj
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D34247