force fallback to xsi for correct musl strerror
--
diff --git a/src/libmongoc/src/libbson/src/bson/bson-error.c b/src/libmongoc/src/libbson/src/bson/bson-error.c
index d16b5fa..69daacd 100644
--- a/src/libmongoc/src/libbson/src/bson/bson-error.c
+++ b/src/libmongoc/src/libbson/src/bson/bson-error.c
@@ -109,7 +109,7 @@ bson_strerror_r (int err_code,  /* IN */
    if (strerror_s (buf, buflen, err_code) != 0) {
       ret = buf;
    }
-#elif defined(__GNUC__) && defined(_GNU_SOURCE)
+#elif 0
    ret = strerror_r (err_code, buf, buflen);
 #else /* XSI strerror_r */
    if (strerror_r (err_code, buf, buflen) == 0) {