Add a package for rust-beta
This package is for NetBSD amd64, a.k.a. x86_64 only!
Everything related to other OSs and/or target platforms has been stripped off.
The beta channel has several iterations along the path to next stable release.
Regenerating checksums may be needed to build the correct rust-beta iteration.
rust194: for now don't make "known target in 'unknown' list" fatal.
The "m68k-unknown-netbsd" entry may be in that list for a while,
until upstream LLVM is fixed to not only emit 16-bit PC-relative
relocations, which are ... inadequate for rust.
This should get rid of this as a fatal error if you need to rebuild
newer rust compilers using older pkgsrc rust compilers, which have
since 1.93 made m68k-unknown-netbsd a "known" target.