[9fans] another compile problem

[erik quanstrom]

SEMSLEEP isn't defined in /sys/src/libc/9syscall/sys.h

; cd $home/nix-os
; grep SEMSLEEP `{find . }
./sys/src/nix/port/syscallfmt.c:        case SEMSLEEP:
./sys/src/nix/port/systab.c:    [SEMSLEEP]      { "Semsleep", syssemsleep, { .i 
= -1 } },

- erik