Remove unused variables.

This fixes the build when using gcc.

Change-Id: I98b9afcf0b40b692e46f92dc4b71583e41877281
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/34681
Auto-Submit: dan sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
diff --git a/src/writer/hlsl/generator_impl.cc b/src/writer/hlsl/generator_impl.cc
index 2b66d3f..dc91175 100644
--- a/src/writer/hlsl/generator_impl.cc
+++ b/src/writer/hlsl/generator_impl.cc
@@ -1977,7 +1977,7 @@
   if (auto* d = stmt->As<ast::DiscardStatement>()) {
     return EmitDiscard(out, d);
   }
-  if (auto* f = stmt->As<ast::FallthroughStatement>()) {
+  if (stmt->As<ast::FallthroughStatement>()) {
     make_indent(out);
     out << "/* fallthrough */" << std::endl;
     return true;
diff --git a/src/writer/msl/generator_impl.cc b/src/writer/msl/generator_impl.cc
index 1161be7..6fa0c6a 100644
--- a/src/writer/msl/generator_impl.cc
+++ b/src/writer/msl/generator_impl.cc
@@ -1736,7 +1736,7 @@
   if (auto* d = stmt->As<ast::DiscardStatement>()) {
     return EmitDiscard(d);
   }
-  if (auto* f = stmt->As<ast::FallthroughStatement>()) {
+  if (stmt->As<ast::FallthroughStatement>()) {
     make_indent();
     out_ << "/* fallthrough */" << std::endl;
     return true;