Feature/zephyr ztest (#118)

* Leverage (older) embedded unit tests into external unit tests build upon copy of Zephyr's ztest library and CMake.

* Expand top-level CMake build to run external unit tests.

* Expand Zephyr module extension to run external unit tests via west or sanitycheck.

Co-authored-by: Gregory Shue <gregory.shue@legrand.us>

test/ztest/include/zephyr.h

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2015 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_ZEPHYR_H_
+#define ZEPHYR_INCLUDE_ZEPHYR_H_
+
+/*
+ * Applications can identify whether they are built for Zephyr by
+ * macro below. (It may be already defined by a makefile or toolchain.)
+ */
+#ifndef __ZEPHYR__
+#define __ZEPHYR__
+#endif
+
+//GAS: rm? #include <kernel.h>
+
+//GAS: add?
+#define Z_STRINGIFY(x) #x
+#define STRINGIFY(s) Z_STRINGIFY(s)
+
+#endif /* ZEPHYR_INCLUDE_ZEPHYR_H_ */