This is basically a backport of the following commits + replacing
xalloc/xfree by malloc/free. Fixes ArcticaProject/nx-libs#358.

   commit 2761c103311a1160bc483fd0367d654733df8598
   Author: Daniel Stone <daniel@fooishbar.org>
   Date:   Mon Nov 5 14:03:26 2007 +0000

       OS: Remove usage of alloca

       Replace with heap allocations.

   commit 5e363500c86042c394595e1a6633581eb8fcd1bb
   Author: Daniel Stone <daniel@fooishbar.org>
   Date:   Mon Nov 5 14:38:28 2007 +0000

       OS: Remove ALLOCATE_LOCAL from os.h

       Remove ALLOCATE_LOCAL_FALLBACK and DEALLOCATE_LOCAL_FALLBACK from os.h, and
       remove the include of Xalloca.h as well.