118b50524b
Rename all remaining compiler crates to use the `rustc_foo` pattern libarena -> librustc_arena libfmt_macros -> librustc_parse_format libgraphviz -> librustc_graphviz libserialize -> librustc_serialize Closes https://github.com/rust-lang/rust/issues/71177 in particular.
librustc_target contains some very low-level details that are
specific to different compilation targets and so forth.
For more information about how rustc works, see the rustc dev guide.