Add crate for testing build configs (#2326)

I intend to publish this to crates.io after review.

This will be used to test
#2312.

crate_universe/test_data/test_data_passing_crate/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "test_data_passing_crate"
+description = "Used by https://github.com/bazelbuild/rules_rust to test cargo emulation"
+version = "0.1.0"
+edition = "2021"
+repository = "https://github.com/bazelbuild/rules_rust"

crate_universe/test_data/test_data_passing_crate/README.md

@@ -0,0 +1,3 @@
+# test_data_passing_crate
+
+This crate exists, and is published to crates.io, so that we can write tests for crate_universe which assert over what opt level and OUT_DIR were used when third-party crates from crates.io were being built.

crate_universe/test_data/test_data_passing_crate/build.rs

@@ -0,0 +1,10 @@
+fn main() {
+    println!(
+        "cargo:rustc-env=BUILD_SCRIPT_OPT_LEVEL={}",
+        std::env::var("OPT_LEVEL").unwrap()
+    );
+    println!(
+        "cargo:rustc-env=BUILD_SCRIPT_OUT_DIR={}",
+        std::env::var("OUT_DIR").unwrap()
+    );
+}

crate_universe/test_data/test_data_passing_crate/src/lib.rs

@@ -0,0 +1,7 @@
+pub const fn get_opt_level() -> &'static str {
+    env!("BUILD_SCRIPT_OPT_LEVEL")
+}
+
+pub const fn get_out_dir() -> &'static str {
+    env!("BUILD_SCRIPT_OUT_DIR")
+}