Passing arguments through to configure

[Bryan O'Sullivan]

I'm writing bindings for LLVM at the moment, and I'm using autoconf to
ensure that LLVM is really installed, and that the necessary version is
present.

Unfortunately, I can't find any pre-existing examples of how to pass
arguments from Setup configure through to configure.  This is something
I need so that I can build against an SVN build of LLVM, instead of
installing it to /usr/local where it would indeed get found.

What I'd like to be able to do is augment the arguments accepted by
Setup configure to include e.g. --with-llvm=/PREFIX and then pass that
through to ./configure.  After reading the Cabal source for a while, I
eventually noticed --configure-option, but I was hoping to do something
a little more integrated, along the lines of adding a --with-llvm
option.  Is this realistic?  The code doesn't currently seem to be set
up to permit that kind of extensibility.

	<b