posix_memalign introduced in 10.6

--- ./boost/align/detail/aligned_alloc_posix.hpp.orig
+++ ./boost/align/detail/aligned_alloc_posix.hpp
@@ -23,8 +23,10 @@
         alignment = sizeof(void*);
     }
     void* p;
-    if (::posix_memalign(&p, alignment, size) != 0) {
-        p = 0;
+    if (alignment <= 16) {
+        p = ::malloc(size);
+    } else {
+        p = ::valloc(size);
     }
     return p;
 }
