Support hyphens in target names

[dtolnay]

This PR makes it possible to define and depend on Rust targets whose name contains hyphen instead of underscore, primarily intended for case-matching names of third party libraries.

Example:

rust_library(
    name = "thiserror-impl",
    srcs = glob(["vendor/thiserror-impl-1.0.11/src/**/*.rs"]),
    crate_type = "proc-macro",
    deps = [
        "//third-party:proc-macro2",
        "//third-party:quote",
        "//third-party:syn",
    ],
)

Tested with dtolnay/cxx#37.

[mfarrugi]

can remove one more by passing crate_name to L108

[dtolnay]

One of them is ctx.attr.name, the other is ctx.label.name. Are those interchangeable?

[mfarrugi]

I'm 99% sure they are, but not entirely.. I think the difference is that ctx.label is the full label