Restore the download of rust-mingw

The build might otherwise break due to mixing MinGW object files from
rust-std and the local MinGW which might be newer/older than the version
used to build rust-std.

Fixes #48272

src/bootstrap/bootstrap.py

@@ -351,6 +351,11 @@ class RustBuild(object):
             with open(self.rustc_stamp(), 'w') as rust_stamp:
                 rust_stamp.write(self.date)
 
+            if "pc-windows-gnu" in self.build:
+                filename = "rust-mingw-{}-{}.tar.gz".format(
+                    rustc_channel, self.build)
+                self._download_stage0_helper(filename, "rust-mingw")
+
         if self.cargo().startswith(self.bin_root()) and \
                 (not os.path.exists(self.cargo()) or
                  self.program_out_of_date(self.cargo_stamp())):