[Refactor] Cleanup isl code generation
Summary:
+ Refactor the runtime check (RTC) build function
+ Added helper function to create an PollyIRBuilder
+ Change the simplify region function to create not
only unique entry and exit edges but also enfore that
the entry edge is unconditional
+ Cleaned the IslCodeGeneration runOnScop function:
- less post-creation changes of the created IR
+ Adjusted and added test casesReviewers: grosser, sebpop, simbuerg, dpeixott
Subscribers: llvm-commits, #polly
Differential Revision: http://reviews.llvm.org/D5076