rr wants to build itself with 32+64bit support on 64bit systems, but
this fails in recent NixOS versions as it can't find libstdc++.so.6 at
runtime.
This patch disables 32bit builds on 64bit. To debug 32bit binaries,
pkgsi686Linux.rr can be used.
This reverts commit 12a3db89ba68ff8f142477e729694fb91fed85c5.
The prior commit was broken a bit; rr will take a little more work to
support a 64bit build.
The git version of `rr` recently got 64bit support; bump version and
pick out a working git revision for the new builds.
Signed-off-by: Austin Seipp <aseipp@pobox.com>
