tools/nolibc: provide the portable sys/select.h

tools/nolibc: provide the portable sys/select.h

Modern programs tend to include sys/select.h to get FD_SET() and
FD_CLR() definitions as well as struct fd_set, but in our case it
didn't exist.

The definitions were moved from types.h to sys/select.h, which is
now included from nolibc.h, and the sys_select() definition moved
there as well from sys.h.

Signed-off-by: Willy Tarreau <w@1wt.eu>
[Thomas: adapt to current -next branch]
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>