Remove automatic RPATH - add user rpath support

Make Configure recognise -rpath and -R to support user added rpaths
for OSF1 and Solaris.  For convenience, add a variable LIBRPATH in the
Unix Makefile, which the users can use as follows:

    ./config [options] -Wl,-rpath,\$(LIBRPATH)

Reviewed-by: Rich Salz <rsalz@openssl.org>
(cherry picked from commit fad599f7)