core: add ssrf.h as global product header

ssrf contains macros/includes etc. used in ssrf, but
not related to dives (mainly in dive.h)

currently the header is created to add the macro UNUSED
later it will be used to remove non-dive related items
from dive.h

Signed-off-by: Jan Iversen <jani@apache.org>

core/ssrf.h

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef SSRF_H
+#define SSRF_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+#ifdef __cplusplus
+}
+#else
+
+// Macro to be used for silencing unused parameters
+#define UNUSED(x) (void)x
+#endif
+
+#endif // SSRF_H