Add support for lowering simd if clause to LLVM IR

Scope of changes:
  1) Added new function to generate loop versioning
  2) Added support for if clause to applySimd function
  2) Added tests which confirm that lowering is successful

If ifCond is specified, then collapsed loop is duplicated and if branch
is added. Duplicated loop is executed if simd ifCond is evaluated to false.

Reviewed By: Meinersbur

Differential Revision: https://reviews.llvm.org/D129368



Signed-off-by: Dominik Adamski <dominik.adamski@amd.com>