bootstrap: Remove usage of RUSTC_TARGET_LINKER

Cargo has a native enviroment variable for this.

src/bootstrap/bin/rustc.rs

@@ -148,11 +148,6 @@ fn main() {
             cmd.arg("-L").arg(&root);
         }
 
-        // Override linker if necessary.
-        if let Ok(target_linker) = env::var("RUSTC_TARGET_LINKER") {
-            cmd.arg(format!("-Clinker={}", target_linker));
-        }
-
         // If we're compiling specifically the `panic_abort` crate then we pass
         // the `-C panic=abort` option. Note that we do not do this for any
         // other crate intentionally as this is the only crate for now that we

src/bootstrap/builder.rs

@@ -926,7 +926,8 @@ impl<'a> Builder<'a> {
             cargo.env("RUSTC_HOST_LINKER", host_linker);
         }
         if let Some(target_linker) = self.linker(target) {
-            cargo.env("RUSTC_TARGET_LINKER", target_linker);
+            let target = crate::envify(&target);
+            cargo.env(&format!("CARGO_TARGET_{}_LINKER", target), target_linker);
         }
         if !(["build", "check", "clippy", "fix", "rustc"].contains(&cmd)) && want_rustdoc {
             cargo.env("RUSTDOC_LIBDIR", self.rustc_libdir(compiler));

src/bootstrap/lib.rs

@@ -1320,3 +1320,13 @@ impl Compiler {
         self.stage >= final_stage
     }
 }
+
+fn envify(s: &str) -> String {
+    s.chars()
+        .map(|c| match c {
+            '-' => '_',
+            c => c,
+        })
+        .flat_map(|c| c.to_uppercase())
+        .collect()
+}

src/bootstrap/test.rs

@@ -23,7 +23,7 @@ use crate::tool::{self, Tool, SourceType};
 use crate::toolstate::ToolState;
 use crate::util::{self, dylib_path, dylib_path_var};
 use crate::Crate as CargoCrate;
-use crate::{DocTests, Mode, GitRepo};
+use crate::{DocTests, Mode, GitRepo, envify};
 
 const ADB_TEST_DIR: &str = "/data/tmp/work";
 
@@ -1913,16 +1913,6 @@ impl Step for CrateRustdoc {
     }
 }
 
-fn envify(s: &str) -> String {
-    s.chars()
-        .map(|c| match c {
-            '-' => '_',
-            c => c,
-        })
-        .flat_map(|c| c.to_uppercase())
-        .collect()
-}
-
 /// Some test suites are run inside emulators or on remote devices, and most
 /// of our test binaries are linked dynamically which means we need to ship
 /// the standard library and such to the emulator ahead of time. This step