Only set CFG_COMPILER_HOST_TRIPLE when building rustc

Author: bjorn3

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

@@ -1378,6 +1378,9 @@ pub fn rustc_cargo_env(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetS
         }
     }
 
+    // The host this new compiler will *run* on.
+    cargo.env("CFG_COMPILER_HOST_TRIPLE", target.triple);
+
     if builder.config.rust_verify_llvm_ir {
         cargo.env("RUSTC_VERIFY_LLVM_IR", "1");
     }

src/bootstrap/src/core/builder/cargo.rs

@@ -1288,8 +1288,6 @@ impl Builder<'_> {
         //
         // FIXME: should update code to not require this env var
 
-        // The host this new compiler will *run* on.
-        cargo.env("CFG_COMPILER_HOST_TRIPLE", target.triple);
         // The host this new compiler is being *built* on.
         cargo.env("CFG_COMPILER_BUILD_TRIPLE", compiler.host.triple);