Pass host flags to rustc shim using prefixed env. vars

Author: Kobzol

src/bootstrap/bin/rustdoc.rs

@@ -48,15 +48,6 @@ fn main() {
     if env::var_os("RUSTC_FORCE_UNSTABLE").is_some() {
         cmd.arg("-Z").arg("force-unstable-if-unmarked");
     }
-    if let Some(linker) = env::var_os("RUSTDOC_LINKER") {
-        let mut arg = OsString::from("-Clinker=");
-        arg.push(&linker);
-        cmd.arg(arg);
-    }
-    if let Ok(no_threads) = env::var("RUSTDOC_LLD_NO_THREADS") {
-        cmd.arg("-Clink-arg=-fuse-ld=lld");
-        cmd.arg(format!("-Clink-arg=-Wl,{no_threads}"));
-    }
     // Cargo doesn't pass RUSTDOCFLAGS to proc_macros:
     // https://github.com/rust-lang/cargo/issues/4423
     // Thus, if we are on stage 0, we explicitly set `--cfg=bootstrap`.

src/bootstrap/builder.rs

@@ -1172,7 +1172,9 @@ impl<'a> Builder<'a> {
         cmd.env_remove("MFLAGS");
 
         if let Some(linker) = self.linker(compiler.host) {
-            cmd.env("RUSTDOC_LINKER", linker);
+            let mut flag = std::ffi::OsString::from("-Clinker=");
+            flag.push(linker);
+            cmd.arg(flag);
         }
         if self.is_fuse_ld_lld(compiler.host) {
             cmd.env("RUSTDOC_FUSE_LD_LLD", "1");

src/bootstrap/test.rs

@@ -854,13 +854,16 @@ impl Step for RustdocTheme {
             .env("RUSTDOC_REAL", builder.rustdoc(self.compiler))
             .env("RUSTC_BOOTSTRAP", "1");
         if let Some(linker) = builder.linker(self.compiler.host) {
-            cmd.env("RUSTDOC_LINKER", linker);
+            let mut flag = std::ffi::OsString::from("-Clinker=");
+            flag.push(linker);
+            cmd.arg(flag);
         }
         if builder.is_fuse_ld_lld(self.compiler.host) {
-            cmd.env(
-                "RUSTDOC_LLD_NO_THREADS",
-                util::lld_flag_no_threads(self.compiler.host.contains("windows")),
-            );
+            cmd.arg("-Clink-arg=-fuse-ld=lld");
+            cmd.arg(format!(
+                "-Clink-arg=-Wl,{}",
+                util::lld_flag_no_threads(self.compiler.host.contains("windows"))
+            ));
         }
         builder.run_delaying_failure(&mut cmd);
     }