Hi Simon,
Mainly this is due to modularity: many of the library packages can be built entirely separately from GHC, so their configure scripts are designed to be standalone.
Yes, I guess it would be a fair bit of work to have it check that you are building the whole of GHC as opposed to separate modules. I just thought that it could check to see if it was a global build -- and share configure checks where appropriate; or, in separate module builds the configure runs as normally.
I know that configure takes a long time on Windows, but I'm surprised if it's a bottleneck for other platforms. How long does the build take? Have you taken steps to speed up the build as described in the Building Guide?
Configuring and building on my Mac can take several hours. Mind you, it's a slow machine (G4 1.33 with 1 gig of RAM). I can safely say it's very fast on my linux machine - the configure whips through, and even a full build only takes a little more than an hour or so. Thanks for pointing out tips to speed up the build. I must confess my ignorance of not checking that! Kind regards, Chris.