[ASan] Do not protect the malloc zone created by malloc_zone_create() on Snow Leopard and earlier systems.
Fixes https://code.google.com/p/address-sanitizer/issues/detail?id=208


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@185621 91177308-0d34-0410-b5e6-96231b3b80d8