rust: enable vendor (#42365)

* rust: enable vendor

* rust: modify vendor description; move the call of variant

* rust: fix style

* rust: typo

* rust: remove variant 'vendor' to let vendoring as default fonctionality

---------

Co-authored-by: LydDeb <lyderic.debusschere@eolen.com>

var/spack/repos/builtin/packages/rust/package.py

@@ -165,6 +165,9 @@ def configure(self, spec, prefix):
         # Compile tools into flag for configure.
         flags.append(f"--tools={','.join(tools)}")
 
+        # Use vendored resources to perform offline build.
+        flags.append("--enable-vendor")
+
         configure(*flags)
 
     def build(self, spec, prefix):