Rollup merge of #34081 - RustOS-Fork-Holding-Ground:no-core-build-script, r=alexcrichton

No build.rs for libcore

I did a grep and there are no longer any mention of "rustbuild" in core, in `cfg`s or otherwise.

src/libcore/Cargo.toml

@@ -2,7 +2,6 @@
 authors = ["The Rust Project Developers"]
 name = "core"
 version = "0.0.0"
-build = "build.rs"
 
 [lib]
 name = "core"

src/libcore/build.rs

@@ -1,17 +0,0 @@
-// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-#![deny(warnings)]
-
-fn main() {
-    // Remove this whenever snapshots and rustbuild nightlies are synced.
-    println!("cargo:rustc-cfg=cargobuild");
-    println!("cargo:rerun-if-changed=build.rs")
-}