By default, all traits in the OpenMP context selector have to match for
it to be acceptable. Though, we sometimes want a single property out of
multiple to match (=any) or no match at all (=none). We offer these
choices as extensions via
`implementation={extension(match_{all,any,none})}`
to the user. The choice will affect the entire context selector not only
the traits following the match property.
The first user will be D75788. There we can replace
```
#pragma omp begin declare variant match(device={arch(nvptx64)})
#define __CUDA__
#include <__clang_cuda_cmath.h>
// TODO: Hack until we support an extension to the match clause that allows "or".
#undef __CLANG_CUDA_CMATH_H__
#undef __CUDA__
#pragma omp end declare variant
#pragma omp begin declare variant match(device={arch(nvptx)})
#define __CUDA__
#include <__clang_cuda_cmath.h>
#undef __CUDA__
#pragma omp end declare variant
```
with the much simpler
```
#pragma omp begin declare variant match(device={arch(nvptx, nvptx64)}, implementation={extension(match_any)})
#define __CUDA__
#include <__clang_cuda_cmath.h>
#undef __CUDA__
#pragma omp end declare variant
```
Reviewed By: mikerice
Differential Revision: https://reviews.llvm.org/D77414
Johannes Doerfert