minor, add HB_USE_INTERNAL_QSORT

The only thing I need for a working wasm in a minimum libc,
otherwise I have to provide the very same qsort inside that libc

src/hb-algs.hh

 /*
  * Copyright © 2017  Google, Inc.
- * Copyright © 2019  Google, Inc.
+ * Copyright © 2019  Facebook, Inc.
  *
  *  This is part of HarfBuzz, a text shaping library.
  *
@@ -843,7 +843,7 @@ static inline void
 hb_qsort (void *base, size_t nel, size_t width,
 	  int (*compar)(const void *_a, const void *_b))
 {
-#ifdef __OPTIMIZE_SIZE__
+#if defined(__OPTIMIZE_SIZE__) && !defined(HB_USE_INTERNAL_QSORT)
   qsort (base, nel, width, compar);
 #else
   sort_r_simple (base, nel, width, compar);