cargo_env = ["CARGO_CRATE_NAME"]

Summary:
I need this for buckifying the next version of rustc after [rust-lang/rust#137834](rust-lang/rust#137834) *"rustc_fluent_macro: use CARGO_CRATE_NAME instead of CARGO_PKG_NAME"*

For a Cargo package like this:

```
[package]
name = "foo-bar"

[lib]
name = "baz-quux"
```

the CARGO_PKG_NAME is "foo-bar" (with hyphen) and the CARGO_CRATE_NAME is "baz_quux" (with underscore).

https://www.internalfb.com/code/fbsource/[b006779c8e495cf1b16de10324d20a1e61259cb9]/fbcode/common/rust/tools/reindeer/src/fixups.rs?lines=875-877%2C922

Reviewed By: diliop

Differential Revision: D73134016

fbshipit-source-id: 494b48d16ab0c3d18132c0a2d190962393453b38

Author: David Tolnay

src/fixups.rs

@@ -872,6 +872,9 @@ impl<'meta> Fixups<'meta> {
 
             for cargo_env in config.cargo_env.iter() {
                 let v = match cargo_env {
+                    CargoEnv::CARGO_CRATE_NAME => {
+                        StringOrPath::String(self.target.name.replace('-', "_"))
+                    }
                     CargoEnv::CARGO_MANIFEST_DIR => {
                         if matches!(self.config.vendor, VendorConfig::Source(_))
                             || matches!(self.package.source, Source::Local)

src/fixups/config.rs

@@ -262,6 +262,7 @@ pub enum CargoEnvs {
 )]
 #[allow(non_camel_case_types)]
 pub enum CargoEnv {
+    CARGO_CRATE_NAME,
     CARGO_MANIFEST_DIR,
     CARGO_PKG_AUTHORS,
     CARGO_PKG_DESCRIPTION,