Add support for hosted test environments

Add a new hosted test environment "processor".

This is meant as a build target used when the
code is not built for a real target
but as part of a test in a hosted environment
(for ex. as a test environment like Zephyr's
native_sim target).

When building for this target PROJECT_PROCESSOR
should be set as "hosted".

In this, the "metal_sleep_usec()" call
is expected to be provided by the system folder
headers.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

lib/processor/hosted/CMakeLists.txt

@@ -0,0 +1,2 @@
+collect (PROJECT_LIB_HEADERS atomic.h)
+collect (PROJECT_LIB_HEADERS cpu.h)

lib/processor/hosted/atomic.h

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2023 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+/*
+ * @file	hosted/atomic.h
+ * @brief	Hosted environment atomic primitives for libmetal.
+ */
+
+#ifndef __METAL_HOSTED_ATOMIC__H__
+#define __METAL_HOSTED_ATOMIC__H__
+
+#endif /* __METAL_HOSTED_ATOMIC__H__ */

lib/processor/hosted/cpu.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2023 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+/*
+ * @file	hosted/cpu.h
+ * @brief	Hosted environment CPU specific primitives
+ */
+
+#include <metal/sys.h>
+
+#ifndef __METAL_HOSTED_CPU__H__
+#define __METAL_HOSTED_CPU__H__
+
+static inline void metal_cpu_yield(void)
+{
+	metal_wait_usec();
+}
+
+#endif /* __METAL_HOSTED_CPU__H__ */