Auto merge of #1022 - sfackler:phys-pages, r=alexcrichton
Auto merge of #1022 - sfackler:phys-pages, r=alexcrichton

Add _SC_PHYS_PAGES on macOS

rust-lang-nursery/libc,rust-lang-nursery/libc,rust-lang-nursery/libc,rust-lang/libc,rust-lang/libc,rust-lang/libc