The _SC_PHYS_PAGES and _SC_AVPHYS_PAGES are not POSIX sysconf values, so
the standart C libraries have no obligation to support it, even on
Linux. Use the Linux sysinfo() system call instead.
PR-URL: https://github.com/libuv/libuv/pull/901
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>