bootstrap: add rust_lld_enabled cfg when rust.lld is enabled in config

Author: lqd

src/bootstrap/compile.rs

@@ -694,6 +694,9 @@ pub fn rustc_cargo_env(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetS
         cargo.rustflag("--cfg=parallel_compiler");
         cargo.rustdocflag("--cfg=parallel_compiler");
     }
+    if builder.config.lld_enabled {
+        cargo.rustflag("--cfg=rust_lld_enabled");
+    }
     if builder.config.rust_verify_llvm_ir {
         cargo.env("RUSTC_VERIFY_LLVM_IR", "1");
     }

src/bootstrap/lib.rs

@@ -194,6 +194,7 @@ const EXTRA_CHECK_CFGS: &[(Option<Mode>, &'static str, Option<&[&'static str]>)]
     (None, "bootstrap", None),
     (Some(Mode::Rustc), "parallel_compiler", None),
     (Some(Mode::ToolRustc), "parallel_compiler", None),
+    (Some(Mode::Rustc), "rust_lld_enabled", None),
     (Some(Mode::Std), "stdarch_intel_sde", None),
     (Some(Mode::Std), "no_fp_fmt_parse", None),
     (Some(Mode::Std), "no_global_oom_handling", None),