rust-xgboost doesn't build on Mac OS

[Lev Kokotov]

rust-xgboost from our fork in postgresml/rust-xgboost doesn't build on Mac OS since the migration to v2.0.

To reproduce on a Mac:

1. Checkout the repo postgresml/rust-xgboost
2. git submodule update --init --recursive
3. cargo build

An error similar to:

    |
365 |     pub static std_value: _Tp;
    |                           ^^^ not found in this scope

will appear.

Reverting to commit 3d4bd10b70117b94367d3c300d233252a204061d fixes the compilation issue.

[Lev Kokotov]

I went into the bindgen-generated file in postgresml/pgml-extension/target/debug/build/xgboost-sys-00829db49cff0fdf/out/bindings.rs:365:27 (your path will differ, but it'll be in the error message) and manually removed:

extern "C" {
    #[link_name = "\u{1}value"]
    pub static std_value: _Tp;
}

This worked and compiled and ran fine.