Use named constant to indicate all lanes, to handle 32 and 64 wide architectures

Summary: Use named constant to indicate all lanes, to handle 32 and 64 wide architectures

Reviewers: ABataev, jdoerfert, grokos, ronlieb

Reviewed By: grokos

Subscribers: ronlieb, openmp-commits

Tags: #openmp

Differential Revision: https://reviews.llvm.org/D68369

git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@373793 91177308-0d34-0410-b5e6-96231b3b80d8