Make sure Alloy src still downloaded even for binary builds

Author: jacob-hughes

build.py

@@ -651,7 +651,7 @@ def cmd_args(self):
 
     def build(self, c, target_dir, install_dir, bench_cfg_bin, profile, env):
         self.FD.fetch()
-        ALLOY.fetch()
+        ALLOY.repo.fetch()
         cargo_build(
             c,
             self.FD.src,