Fuzzers: Avoid passing target backend as parameter

Changes various fuzz targets so that the target back-end language (HLSL,
MSL, SPIR-V or WGSL) is no longer passed as a command line argument, but
instead baked into the fuzzer's binary. This avoids a problem whereby a
ClusterFuzz bug reproducer does not use the required back-end command
line argument.

Change-Id: I64402a23391ca0f24c9d1ffd2aa2f218cc7106b1
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/63163
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ryan Harrison <rharrison@chromium.org>
Commit-Queue: Alastair Donaldson <afdx@google.com>

fuzzers/tint_regex_fuzzer/tint_regex_spv_writer_fuzzer.cc

@@ -0,0 +1,33 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <cassert>
+
+#include "fuzzers/tint_regex_fuzzer/cli.h"
+#include "fuzzers/tint_regex_fuzzer/override_cli_params.h"
+
+namespace tint {
+namespace fuzzers {
+namespace regex_fuzzer {
+
+void OverrideCliParams(CliParams& cli_params) {
+  assert(cli_params.fuzzing_target == FuzzingTarget::kAll &&
+         "The fuzzing target should not have been set by a CLI parameter: it "
+         "should have its default value.");
+  cli_params.fuzzing_target = FuzzingTarget::kSpv;
+}
+
+}  // namespace regex_fuzzer
+}  // namespace fuzzers
+}  // namespace tint