build-system: cargo: Use correct cargo.

* gnu/packages/rust.scm (cargo-bootstrap): Make private.
* guix/build-system/cargo.scm (default-cargo): Use cargo.

gnu/packages/rust.scm

@@ -122,9 +122,7 @@
 which can in turn be used to build the final Rust compiler.")
     (license license:asl2.0)))
 
-;; FIXME: Make private once cargo is packaged. Is currently used by the
-;; cargo-build-system.
-(define-public cargo-bootstrap
+(define cargo-bootstrap
   (package
     (name "cargo-bootstrap")
     (version (cargo-version %rust-bootstrap-binaries-version))

guix/build-system/cargo.scm

@@ -46,8 +46,7 @@ to NAME and VERSION."
   "Return the default Cargo package."
   ;; Lazily resolve the binding to avoid a circular dependency.
   (let ((rust (resolve-interface '(gnu packages rust))))
-    ;; FIXME: Package cargo and replace cargo-bootstrap with cargo.
-    (module-ref rust 'cargo-bootstrap)))
+    (module-ref rust 'cargo)))
 
 (define (default-rustc)
   "Return the default Rustc package."