Reduce the size of a rust install slightly

Two optimizations:

1. Compress `foo.bc` in each rlib with `flate`. These are just taking up space and are only used with LTO, no need for LTO to be speedy.
2. Stop install `librustc.rlib` and friends, this is a *huge* source of bloat. There's no need for us to install static libraries for these components.

cc #12440