musl: make strtoll() accept strings start with dot

glibc accepts strings start with '.' and returns 0, but musl refuses
them. Let's accept them, as our code assumes the function accept such
strings.

src/include/musl/stdlib.h

@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include_next <stdlib.h>
+
+long long strtoll_fallback(const char *nptr, char **endptr, int base);
+#define strtoll strtoll_fallback