utils: Introduce OSMO_ASSERT in the utils and use it in the unit tests

The tests should unconditionally assert, regardless of debug settings.
This uses the OSMO_ prefix as it's in the global namespace.
diff --git a/include/osmocom/core/utils.h b/include/osmocom/core/utils.h
index 03861d7..8f7bee3 100644
--- a/include/osmocom/core/utils.h
+++ b/include/osmocom/core/utils.h
@@ -51,6 +51,13 @@
 	rem -= ret;						\
 } while (0)
 
+#define OSMO_ASSERT(exp)    \
+	if (!(exp)) { \
+		printf("Assert failed %s %s:%d\n", #exp, __FILE__, __LINE__); \
+		abort(); \
+	}
+
+
 /*! @} */
 
 #endif