Temporarily force substitution of cvdalloc.

Do this for two reasons:

* since the substitution marker file is not updated, cvdalloc must be
  substituted by flag during a `cvd fetch`. This also means since
  cvdalloc is not copied back to the Android repository, cvdalloc is
  missing even when substitution to override (e.g., during development)
  is not desired

* updating the substitution marker file in Android is causing other
  unrelated failures not detected by presubmit, and is blocking
  rollout progress.

Once the substitution marker file change is completed safely, we can
revert this change.

Forced substitution like this should be safe, since cvdalloc is packaged
normally, and substitution unlinks if the target already exists.

Author: 3405691582

base/cvd/cuttlefish/host/commands/cvd/fetch/substitute.cc

@@ -185,6 +185,12 @@ Result<void> HostPackageSubstitution(
     LOG(INFO) << "using local debian substitution marker file: " << marker_file;
   }
 
+  // TODO: remove when we can safely add this to the marker file.
+  std::string cvdalloc_src =
+      fmt::format("{}/bin/{}", CF_EXPECT(GetCuttlefishCommonDir()), "cvdalloc");
+  std::string cvdalloc_name = fmt::format("{}/{}", target_dir, "cvdalloc");
+  CF_EXPECT(Substitute(cvdalloc_src, cvdalloc_name));
+
   if (host_substitutions.empty() && FileExists(marker_file)) {
     CF_EXPECT(SubstituteWithMarker(target_dir, marker_file));
   } else {