[OpenMP][OMPIRBuilder] Add support for order(concurrent) to OMPIRBuilder for SIMD directive

If 'order(concurrent)' clause is specified, then the iterations of SIMD loop
can be executed concurrently.

This patch adds support for LLVM IR codegen via OMPIRBuilder for SIMD loop
with 'order(concurrent)' clause. The functionality added to OMPIRBuilder is
similar to the functionality implemented in 'CodeGenFunction::EmitOMPSimdInit'.

Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D134046



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