Add support for out of source tree compilation.
Hello, it would be good if GHC supports also out of source tree compilation so that files produced during the build will not pollute source tree. E.g.
mkdir obj-ghc cd obj-ghc ../ghc/configure make
Currently configure step complain about:
$ ../ghc/configure mk/config.h.in doesn't exist: perhaps you haven't run 'perl boot'?