The /proc/self/exe path is Linux specific.  We do have /proc/self/path/a.out.

--- libotr-4.1.1/tests/unit/test_instag.c.orig
+++ libotr-4.1.1/tests/unit/test_instag.c
@@ -173,7 +173,7 @@
 {
 	char *path_end;
 
-	if (readlink("/proc/self/exe", buf, len) < 0) {
+	if (readlink("/proc/self/path/a.out", buf, len) < 0) {
 		return -ENOMEM;
 	}