ztest: define test_main in the header file.

This also makes test_main C++ compatible by setting the linkage.

Signed-off-by: Michael Hope <mlhx@google.com>

tests/ztest/include/ztest.h

@@ -13,6 +13,10 @@
 #ifndef __ZTEST_H__
 #define __ZTEST_H__
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /**
  * @defgroup ztest Zephyr testing suite
  */
@@ -49,4 +53,10 @@
 #include <tc_util.h>
 #include <logging/sys_log.h>
 
+void test_main(void);
+
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* __ZTEST_H__ */

tests/ztest/src/ztest.c

@@ -259,8 +259,6 @@ void _ztest_run_test_suite(const char *name, struct unit_test *suite)
 	test_status = (test_status || fail) ? 1 : 0;
 }
 
-void test_main(void);
-
 #ifndef KERNEL
 int main(void)
 {