Build bitcode with zig 🎉

compiler/builtins/src/bitcode.rs

@@ -0,0 +1,18 @@
+use std::fs::File;
+use std::io::prelude::Read;
+use std::vec::Vec;
+
+pub fn get_bytes() -> Vec<u8> {
+    // In the build script for the gen module, we compile the builtins bitcode and set
+    // BUILTINS_BC to the path to the compiled output.
+    let path: &'static str = env!(
+        "BUILTINS_BC",
+        "Env var BUILTINS_BC not found. Is there a problem with the build script?"
+    );
+    let mut builtins_bitcode = File::open(path).expect("Unable to find builtins bitcode source");
+    let mut buffer = Vec::new();
+    builtins_bitcode
+        .read_to_end(&mut buffer)
+        .expect("Unable to read builtins bitcode");
+    buffer
+}