fix macos build issues by specifying enzyme lib dir

Author: ZuseZ4

src/bootstrap/src/core/build_steps/compile.rs

@@ -1092,8 +1092,11 @@ pub fn rustc_cargo(
 
     // We want to link against registerEnzyme and in the future we want to use additional
     // functionality from Enzyme core. For that we need to link against Enzyme.
-    // FIXME(ZuseZ4): Get the LLVM version number automatically instead of hardcoding it.
     if builder.config.llvm_enzyme {
+        let arch = builder.build.build;
+        let enzyme_dir = builder.build.out.join(arch).join("enzyme").join("lib");
+        cargo.rustflag("-L").rustflag(enzyme_dir.to_str().expect("Invalid path"));
+        // FIXME(ZuseZ4): Get the LLVM version number automatically instead of hardcoding it.
         cargo.rustflag("-l").rustflag("Enzyme-19");
     }
 

tests/codegen/autodiff.rs

@@ -1,4 +1,4 @@
-//@ compile-flags: -C opt-level=3  -Clto=fat
+//@ compile-flags: -Zautodiff=Enable -C opt-level=3  -Clto=fat
 //@ no-prefer-dynamic
 //@ needs-enzyme
 #![feature(autodiff)]