pw_minimal_cpp_stdlib: Extremely limited C++ lib

pw_minimal_cpp_stdlib is an extremely limited, non-standard
implementation of the C++ Standard Library. It requires C++17 and a C
standard library.

Change-Id: I2d0b8d6cf49730e2c746eddf2c4a23308af1eb6a
diff --git a/BUILD.gn b/BUILD.gn
index 6379134..355b961 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1,4 +1,4 @@
-# Copyright 2019 The Pigweed Authors
+# Copyright 2020 The Pigweed 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
@@ -54,6 +54,7 @@
     "$dir_pw_base64",
     "$dir_pw_checksum",
     "$dir_pw_kvs",
+    "$dir_pw_minimal_cpp_stdlib",
     "$dir_pw_polyfill",
     "$dir_pw_preprocessor",
     "$dir_pw_protobuf",
@@ -73,6 +74,7 @@
     "$dir_pw_checksum:tests",
     "$dir_pw_kvs:tests",
     "$dir_pw_log:tests",
+    "$dir_pw_minimal_cpp_stdlib:tests",
     "$dir_pw_polyfill:tests",
     "$dir_pw_preprocessor:tests",
     "$dir_pw_protobuf:tests",