rbenv/Ruby 2.1.5 ignoring MacPorts openssl

I have the latest openssl-1.0.1j installed via Macports and visible on
my PATH but even if I specify:

RUBY_CONFIGURE_OPTS=–with-openssl-dir=/opt/local/bin

… or

RUBY_CONFIGURE_OPTS=–with-openssl-dir=/opt/local

… rbenv insists on installing its own version of the same thing when I
run:

rbenv install 2.1.5

Same with earlier Ruby versions.

gvim