Move polly options into separate option category

Use the new cl::OptionCategory support to move the Polly options into a separate
option category. The aim is to hide most options and show by default only the
options a user needs to influence '-O3 -polly'. The available options probably
need some care, but here is the current status:

Polly Options:
Configure the polly loop optimizer

  -enable-polly-openmp              - Generate OpenMP parallel code
  -polly                            - Enable the polly optimizer (only at -O3)
  -polly-no-tiling                  - Disable tiling in the scheduler
  -polly-only-func=<function-name>  - Only run on a single function
  -polly-report                     - Print information about the activities
                                      of Polly
  -polly-vectorizer                 - Select the vectorization strategy
    =none                           -   No Vectorization
    =polly                          -   Polly internal vectorizer
    =unroll-only                    -   Only grouped unroll the vectorize
                                        candidate loops
    =bb                             -   The Basic Block vectorizer driven by
                                        Polly

llvm-svn: 181295