Information on build.mk during boot and configure

At the moment both ./boot and ./configure.ac contain information about build.mk This seems a bit outdated. Both these scripts are being used whether using make or hadrian later on

https://github.com/ghc/ghc/blob/master/boot#L188-L201 https://github.com/ghc/ghc/blob/master/configure.ac#L1462-L1470

1. WARNING: You don't have a mk/build.mk file. in boot and For a standard build of GHC (fully optimised with profiling), type (g)make. in configure.ac doesn't seem to take into account hadrian build system
2. Both boot By default a standard GHC build will be done and configure For a standard build of GHC point to a standard build, but each of them gives slightly different (and useful) information about it. This is basically the same topic/message so why spread it out over 2 scripts? Maybe but both information in both scripts or just in one script.

I was about to rewrite some of this in-script documentation, but i'm not sure what info to place where under which condition.