Require compiler-rt root at ../src/llvm-project/compiler-rt

src/bootstrap/compile.rs

@@ -186,6 +186,8 @@ pub fn std_cargo(builder: &Builder<'_>, target: Interned<String>, cargo: &mut Ca
     // `compiler-rt` is located.
     let compiler_builtins_root = builder.src.join("src/llvm-project/compiler-rt");
     let compiler_builtins_c_feature = if compiler_builtins_root.exists() {
+        // Note that `libprofiler_builtins/build.rs` also computes this so if
+        // you're changing something here please also change that.
         cargo.env("RUST_COMPILER_RT_ROOT", &compiler_builtins_root);
         " compiler-builtins-c".to_string()
     } else {

src/libprofiler_builtins/build.rs

@@ -63,8 +63,9 @@ fn main() {
         cfg.define("COMPILER_RT_HAS_ATOMICS", Some("1"));
     }
 
-    let root = env::var_os("RUST_COMPILER_RT_ROOT").unwrap();
-    let root = Path::new(&root);
+    // Note that this should exist if we're going to run (otherwise we just
+    // don't build profiler builtins at all).
+    let root = Path::new("../llvm-project/compiler-rt");
 
     let src_root = root.join("lib").join("profile");
     for src in profile_sources {