Do not allow to complex branch conditions

  Even before we build the domain the branch condition can become very
  complex, especially if we have to build the complement of a lot of
  equality constraints. With this patch we bail if the branch condition
  has a lot of basic sets and parameters.

  After this patch we now successfully compile
    External/SPEC/CINT2000/186_crafty/186_crafty
  with "-polly-process-unprofitable -polly-position=before-vectorizer".

llvm-svn: 265286