Add setup-buildx action (#71)

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

setup-buildx/src/state-helper.ts

@@ -0,0 +1,14 @@
+// From https://github.com/actions/checkout/blob/master/src/state-helper.ts
+
+import * as coreCommand from '@actions/core/lib/command';
+
+/**
+ * Indicates whether the POST action is running
+ */
+export const IsPost = !!process.env['STATE_isPost'];
+
+// Publish a variable so that when the POST action runs, it can determine it should run the cleanup logic.
+// This is necessary since we don't have a separate entry point.
+if (!IsPost) {
+  coreCommand.issueCommand('save-state', {name: 'isPost'}, 'true');
+}