bootstrap: build std with less frame pointers

Sometimes leaf frame-pointers can impact LLVM inlining choices, and
that can be a real problem for things like `mul_add`.

Author: workingjubilee

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

@@ -670,7 +670,8 @@ pub fn std_cargo(builder: &Builder<'_>, target: TargetSelection, stage: u32, car
 
     // Enable frame pointers by default for the library. Note that they are still controlled by a
     // separate setting for the compiler.
-    cargo.rustflag("-Cforce-frame-pointers=yes");
+    cargo.rustflag("-Zunstable-options");
+    cargo.rustflag("-Cforce-frame-pointers=non-leaf");
 
     let html_root =
         format!("-Zcrate-attr=doc(html_root_url=\"{}/\")", builder.doc_rust_lang_org_channel(),);