Rustc update to 1.78.0

[nieder]

bump to 1.78.0
Package includes cargo, which used to be a separate package, but cargo 0.79.0 is included as part of 1.78.0 dist
I was able to build a couple sample .rs files with this, and cargo was able to download some crates and use them to compile another thing.

[nieder]

So the dylibs created by rustc include a hash in the filename that's unique to the compiler settings and host. Therefore, doesn't seem to generate a reproducible build. Ugh.

[nieder]

I take that back. Tried building on 10.14.6 and 12.7, and in both cases the hash on the dylibs was the same. So maybe it's just dependent on build settings.

[dmacks]

It would be great to get rust on apple-silicon. There are no "arm64-apple-darwin" bootstrap files on their server (based on %m), but there are "aarch64-apple-darwin" files. I guess we need separate .info or a Type: token for the arch string it ants conditional on %m rather than using %m directly.

Not a blocker because our existing rustc is also hardcoded to x86_64, but I don't have an x86_64 sandbox at the moment to test.

[nieder]

Can you conditional some of the Type: entries on %m?

Type: <<
   ( %m = "x86_64" ) bootstrap_arch (x86_64),
   ( %m = "arm64" ) bootstrap_arch (aarch64),
   bootstrap_d (2024-03-21),
   bootstrap_v (1.77.0),
   llvm_v (16)
<<