Use rustbuild instead of the old makefiles. Update bootstrapping to include rust-std and cargo. Add a rust-lldb subpackage.
Require rust-rpm-macros for new crate packaging. Keep shared libraries under rustlib/, only debug-stripped. Merge and clean up conditionals for epel7.
Rewrite bootstrap logic to target specific arches. Bootstrap ppc64, ppc64le, s390x. (thanks to Sinny Kumari for testing!)