freebsd: Provide a dummy backtrace implementation that does nothing
diff --git a/src/backtrace.c b/src/backtrace.c
index 189a3ce..023671c 100644
--- a/src/backtrace.c
+++ b/src/backtrace.c
@@ -57,4 +57,8 @@
 
 	free(strings);
 }
+#else
+void osmo_generate_backtrace(void)
+{
+}
 #endif