Drop EXTFLAG and lib references

They are picked up automatically now.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
configure: auto-generate a config-host.h

Don't have all these special cases to convert a .mak to a .h define,
just generate it from the configure script instead.

Signed-off-by: Jens Axboe <axboe@kernel.dk>