Follow changes in GHC build system
Revert DPH phase numbers.
Temporarily comment out the vectorisation of 'undefined'

I've emailed Manuel about this... nothing fundamental here,
just a glitch
Allow dph to be disabled
Fix warnings
Adapt to new version of the vector library.
Add support for using SIMD vector operations.
Add a multi-enabled version of the Double Prelude.
Fix for vectorization avoidance.