[OpenMP][OMPIRBuilder] Move SIMD alignment calculation to LLVM Frontend

Currently default simd alignment is specified by Clang specific TargetInfo
class. This class cannot be reused for LLVM Flang. If we move the default
alignment field into TargetMachine class then we can create TargetMachine
objects and query them to find SIMD alignment.

Scope of changes:
  1) Added information about maximal allowed SIMD alignment to TargetMachine
     classes.
  2) Removed getSimdDefaultAlign function from Clang TargetInfo class.
  3) Refactored createTargetMachine function.

Reviewed By: jsjodin

Differential Revision: https://reviews.llvm.org/D138496