https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80836
--- Comment #1 from René J.V. Bertin <rjvbertin at gmail dot com> --- I found some suggestions here http://stackoverflow.com/questions/13813737/how-can-i-set-rpath-on-gcc-binaries-during-bootstrap which I haven't yet been able to check (a full build runs overnight on my hardware). It seems though that this is a sufficiently likely issue to warrant a dedicated --with-rpath option. Especially since --with-stage1-ldflags (and --with-bootstrap-ldflags) have a platform-specific default that apparently gets overridden instead of completed by the user-supplied value.
