use -R not -Wl,-rpath on FreeBSD

in some cases -Wl,-rpath can be passed to the linker directly instead of
going through gcc (ncurses) and on FreeBSD this causes the linker to
throw an error.  since both gcc and ld on FreeBSD understand -R (directory)
to set the rpath use this instead.
Merge pull request #248 from opscode/lcg/freebsd-opts

use -R not -Wl,-rpath on FreeBSD