Enable compiling on GCC < 5 (#2149)

_ISOC11_SOURCE is the preprocessor flag that specifies whether or not aligned_alloc is defined and exists. While GCC versions lower than 5 do include C++11 and C++14 constructs, they do not include std::aligned_alloc, so this check allows compiling on those versions of GCC by defaulting down to posix_memalign in those situations appropriately.

Author: zeroshade

src/support/alloc.h

@@ -38,7 +38,7 @@ inline void* aligned_malloc(size_t align, size_t size) {
   if (errno == ENOMEM)
     ret = nullptr;
   return ret;
-#elif defined(__APPLE__)
+#elif defined(__APPLE__) || !defined(_ISOC11_SOURCE)
   void* ptr;
   int result = posix_memalign(&ptr, align, size);
   return result == 0 ? ptr : nullptr;