Now when using CPP you get 

   MIN_VERSION_<package>(A,B,C)

for each <package> in build-depends, which is true if the version of
<package> in use is >= A.B.C, using the normal ordering on version
numbers.

This is done by auto-generating a header file
dist/build/autogen/cabal_macros.h, and passing a -include flag when
running CPP.