Starting to think about toolchain semantic analysis -- create a trivial shell for it. (#1038)

toolchain/semantics/semantics.cpp

@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include "toolchain/semantics/semantics.h"
+
+namespace Carbon {
+
+Semantics Semantics::Analyze(const ParseTree& parse_tree,
+                             DiagnosticConsumer& consumer) {
+  Semantics semantics;
+  return semantics;
+}
+
+}  // namespace Carbon