Build fixes

Two incompatible changes landed simultaniously.
Also fix a warning about variable shadowing.

Change-Id: I84c9ba48fb87a348a5b0e622ca2fdb191f95a6b2
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/49964
Commit-Queue: Ben Clayton <bclayton@google.com>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Auto-Submit: Ben Clayton <bclayton@google.com>
Reviewed-by: Ryan Harrison <rharrison@chromium.org>
diff --git a/src/resolver/resolver.cc b/src/resolver/resolver.cc
index 488bc6c..e098271 100644
--- a/src/resolver/resolver.cc
+++ b/src/resolver/resolver.cc
@@ -397,6 +397,9 @@
       }
       return nullptr;
     }
+    if (auto* t = ty->As<ast::ExternalTexture>()) {
+      return builder_->create<sem::ExternalTexture>();
+    }
     if (auto* t = ty->As<ast::TypeName>()) {
       auto it = named_types_.find(t->name());
       if (it == named_types_.end()) {