use env var to enable self-contained linker

Author: lqd

compiler/rustc_target/src/spec/targets/x86_64_unknown_linux_gnu.rs

@@ -18,10 +18,9 @@ pub fn target() -> Target {
         | SanitizerSet::THREAD;
     base.supports_xray = true;
 
-    #[cfg(use_rust_lld)]
-    {
-        // When we're asked to use the `rust-lld` linker by default, set the appropriate lld-using
-        // linker flavor, and self-contained linker component.
+    // When we're asked to use the `rust-lld` linker by default, set the appropriate lld-using
+    // linker flavor, and self-contained linker component.
+    if option_env!("CFG_USE_SELF_CONTAINED_LINKER").is_some() {
         base.linker_flavor = LinkerFlavor::Gnu(Cc::Yes, Lld::Yes);
         base.link_self_contained = crate::spec::LinkSelfContainedDefault::with_linker();
     }

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

@@ -1129,10 +1129,9 @@ pub fn rustc_cargo_env(
         cargo.env("CFG_DEFAULT_LINKER", s);
     }
 
-    // Enable rustc's cfgs for `rust-lld` when requested.
+    // Enable rustc's env var for `rust-lld` when requested.
     if builder.config.lld_enabled {
-        cargo.rustflag("--cfg=use_rust_lld");
-        cargo.rustdocflag("--cfg=use_rust_lld");
+        cargo.env("CFG_USE_SELF_CONTAINED_LINKER", "1");
     }
 
     if builder.config.rust_verify_llvm_ir {