physmem: use sysinfo if _SC_PHYS_PAGES unavailable * lib/physmem.c (physmem_total): Some systems like musl libc do not (yet) support _SC_PHYS_PAGES. Use the linux syscall sysinfo as fallback if _SC_PHYS_PAGES or _SC_PAGESIZE fails. (physmem_available): Likewise for _SC_AVPHYS_PAGES. Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>