Register Polly passes automatically

Polly adds, after it is loaded into opt or clang, its passes to the default set
of -O3 passes. This means optimizing a program with clang and Polly becomes as
simple as executing.

clang -Xclang -load -Xclang lib/LLVMPolly.so -O3 program.c

The same should work for dragonegg powered gfortran, g++, ... or any other tool
that uses the PassManagerBuilder.

Warning: Even though using Polly became with this commit extremly easy, Polly
         is still Pre-Alpha Quality. This means in most cases it will rather
         destroy the world than doing anything positive. ;-)
llvm-svn: 138402