Prepare for crates.io inclusion into libstd

See rust-lang/rust#56092

Author: alexcrichton

Cargo.toml

@@ -21,6 +21,12 @@ test = false
 [target.'cfg(all(unix, not(target_arch = "wasm32")))'.dependencies]
 libc = { version = "0.2", default-features = false }
 
+[dependencies]
+# For more information on these dependencies see rust-lang/rust's
+# `src/tools/rustc-std-workspace` folder
+core = { version = '1.0.0', optional = true, package = 'rustc-std-workspace-core' }
+compiler_builtins = { version = '0.1.0', optional = true }
+
 [dev-dependencies]
 rand = "0.3"
 
@@ -37,3 +43,4 @@ debug = []
 
 # Enable experimental support for the standard library's unstable allocator API.
 allocator-api = []
+rustc-dep-of-std = ['core', 'compiler_builtins/rustc-dep-of-std']