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Partly this is cleaner as we only have to preprocess the source files
once, but also it is necessary to avoid Haddock recompiling source
files when Template Haskell is in use, saving some time in validate
and fixing a problem whereby when HADDOCK_DOCS=YES, make always
re-haddocks the DPH packages.  This also needs an additional fix to
GHC.

HsColour support still uses Cabal, and hence preprocesses the source
files again. We could move this into the build system too, but there
is a version dependency that would mean adding extra autoconf stuff.

Also tidied up the way configure.ac gets into bindists

We now just call gcc to get the dependencies directly

This is a rerecord of
    Stephen Blackheath <oversensitive.pastors.stephen@blacksapphire.com>**20090930222855
to avoid conflicts.

This meakes it easier to correctly clean libffi

So we don't try to recreate directories just because they are older
than mkdirhier, since mkdirhier won't touch them.

And add a comment explaining why these options are here

You can now have multiple versions of a package installed, and
gen_contents_index will do the right thing.

This means that we get the right program name in error messages etc.

See comments for details.

This means we can remove some conditional stuff from the Makefiles,
and means the testsuite doesn't have to work out whether or not it's
on Windows.

There is now less makefile code duplication.
Also, stage2 packages are registered after GHC, which is important as
they might depend on the ghc package (as dph now does).

We now use an msys/mingw perl tarball

This is the case on Windows (as we have no shell wrappers), and mingw's
shell doesn't like an empty list of things in a "for" command.

Now that we make bindists during validate, we can't assume that ISCC
is available.

To quiet those warnings from make about not being able to delete
directories.

There are now 104 calls to mkdirhier, down from 1201, when validating.