Drop aux_build rustc helpers

They provide very little value and makes it more confusing than is
helpful.

Author: jieyouxu

src/tools/run-make-support/src/external_deps/rustc.rs

@@ -22,12 +22,6 @@ pub fn bare_rustc() -> Rustc {
     Rustc::bare()
 }
 
-/// Construct a new `rustc` aux-build invocation.
-#[track_caller]
-pub fn aux_build() -> Rustc {
-    Rustc::new_aux_build()
-}
-
 /// A `rustc` invocation builder.
 #[derive(Debug)]
 #[must_use]
@@ -76,14 +70,6 @@ impl Rustc {
         Self { cmd, target: None }
     }
 
-    /// Construct a new `rustc` invocation with `aux_build` preset (setting `--crate-type=lib`).
-    #[track_caller]
-    pub fn new_aux_build() -> Self {
-        let mut cmd = setup_common();
-        cmd.arg("--crate-type=lib");
-        Self { cmd, target: None }
-    }
-
     // Argument provider methods
 
     /// Configure the compilation environment.

src/tools/run-make-support/src/lib.rs

@@ -68,7 +68,7 @@ pub use llvm::{
     LlvmFilecheck, LlvmNm, LlvmObjcopy, LlvmObjdump, LlvmProfdata, LlvmReadobj,
 };
 pub use python::python_command;
-pub use rustc::{aux_build, bare_rustc, rustc, rustc_path, Rustc};
+pub use rustc::{bare_rustc, rustc, rustc_path, Rustc};
 pub use rustdoc::{rustdoc, Rustdoc};
 
 /// [`diff`][mod@diff] is implemented in terms of the [similar] library.