Remove configure.ml

[aantron]

In favor of passing options directly to the new discover.ml. See #699.

[aantron]

Usage information for the new discover.ml is found in its code:

lwt/src/unix/config/discover.ml

Lines 27 to 49 in 294b72a

	This program tries to detect everything automatically. If it is not behaving
	correctly, its behavior can be tweaked by passing it arguments. There are
	three ways to do so:
	- By editing [src/unix/dune], to pass arguments to [discover.exe] on the
	command line.
	- By setting the environment variable [LWT_DISCOVER_ARGUMENTS]. The syntax
	is the same as the command line.
	- By writing a file [src/unix/discover_arguments]. The syntax is again the
	same as the command line.
	The possible arguments can be found by running
	{v
	dune exec src/unix/config/discover.exe -- --help
	v}
	In addition, the environment variables [LIBEV_CFLAGS], [LIBEV_LIBS],
	[PTHREAD_CFLAGS], and [PTHREAD_LIBS] can be used to override the flags used
	for compiling with libev and pthreads.
	This [discover.ml] was added in Lwt 4.3.0, so if you pass arguments to
	[discover.ml], 4.3.0 is the minimal required version of Lwt.

[aantron]

configure.ml will be deleted in Lwt 5.0.0, which is to be released around November 2019. It is subsumed by the newly improved discover.ml, which was released just now in Lwt 4.3.0.

If you are using configure.ml, see the new discover.ml usage for how to pass arguments to the configuration process:

lwt/src/unix/config/discover.ml

Lines 27 to 49 in 294b72a

	This program tries to detect everything automatically. If it is not behaving
	correctly, its behavior can be tweaked by passing it arguments. There are
	three ways to do so:
	- By editing [src/unix/dune], to pass arguments to [discover.exe] on the
	command line.
	- By setting the environment variable [LWT_DISCOVER_ARGUMENTS]. The syntax
	is the same as the command line.
	- By writing a file [src/unix/discover_arguments]. The syntax is again the
	same as the command line.
	The possible arguments can be found by running
	{v
	dune exec src/unix/config/discover.exe -- --help
	v}
	In addition, the environment variables [LIBEV_CFLAGS], [LIBEV_LIBS],
	[PTHREAD_CFLAGS], and [PTHREAD_LIBS] can be used to override the flags used
	for compiling with libev and pthreads.
	This [discover.ml] was added in Lwt 4.3.0, so if you pass arguments to
	[discover.ml], 4.3.0 is the minimal required version of Lwt.

If you switch to the new process, you have to use Lwt >= 4.3.0.

cc @fdopen, @toots, @whitequark, in case this is relevant for your cross-compilation repos.

[toots]

Hi! Thanks for the heads up. As far as I can tell we are compiling using the dune mechanism without much change except passing -x windows so, so far, it looks fine on my end (windows cross-compilation).