Add a codegen option to allow loading LLVM pass plugins

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -470,6 +470,8 @@ pub(crate) unsafe fn optimize_with_new_llvm_pass_manager(
 
     let extra_passes = config.passes.join(",");
 
+    let pass_plugins = config.pass_plugins.join(" ");
+
     // FIXME: NewPM doesn't provide a facility to pass custom InlineParams.
     // We would have to add upstream support for this first, before we can support
     // config.inline_threshold and our more aggressive default thresholds.
@@ -499,6 +501,8 @@ pub(crate) unsafe fn optimize_with_new_llvm_pass_manager(
         selfprofile_after_pass_callback,
         extra_passes.as_ptr().cast(),
         extra_passes.len(),
+        pass_plugins.as_ptr().cast(),
+        pass_plugins.len(),
     );
     result.into_result().map_err(|()| llvm_err(diag_handler, "failed to run LLVM passes"))
 }