[tools]: Add intrinsic-gen tool

Parses the intrinsics.def file, then scans the source tree for .tmpl files.
Using both of these, it produces source files for use in tint.

Bug: tint:832
Change-Id: I718114f4c540b9d620899e89d5758f048377ee04
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/52642
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: David Neto <dneto@google.com>

tools/intrinsic-gen

@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+# 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.
+
+set -e # Fail on any error.
+
+if [ ! -x "$(which go)" ] ; then
+    echo "error: go needs to be on \$PATH to use $0"
+    exit 1
+fi
+
+SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}")" >/dev/null 2>&1 && pwd )"
+ROOT_DIR="$( cd "${SCRIPT_DIR}/.." >/dev/null 2>&1 && pwd )"
+BINARY="${SCRIPT_DIR}/bin/intrinsic-gen"
+
+# Rebuild the binary.
+# Note, go caches build artifacts, so this is quick for repeat calls
+pushd "${SCRIPT_DIR}/src/cmd/intrinsic-gen" > /dev/null
+    go build -o "${BINARY}" main.go
+popd > /dev/null
+
+"${BINARY}" "$@"