zstd: synchronize qsort code with upstream

I think we were slightly out of sync with the upstream `dev` branch.
I manually copied stanzas referencing qsort and regenerated the
monolithic source file. I'm pretty sure the state of our qsort code
now agrees with latest upstream.

Closes #277. Hopefully.

Author: indygreg

zstd/zstd.c

@@ -85,8 +85,9 @@
  * header and the script 'combine.sh' combines the whole zstd source code
  * in a single file.
  */
-#if (defined(__linux__) && !defined(__ANDROID__)) || defined(__CYGWIN__) || defined(__MSYS__)
-#ifndef _GNU_SOURCE
+#if defined(__linux) || defined(__linux__) || defined(linux) || defined(__gnu_linux__) || \
+    defined(__CYGWIN__) || defined(__MSYS__)
+#if !defined(_GNU_SOURCE) && !defined(__ANDROID__) /* NDK doesn't ship qsort_r(). */
 #define _GNU_SOURCE
 #endif
 #endif