[OpenMP] NVPTX: Set default/minimum compute capability to sm_35 The current implementation of the nvptx runtime (to be upstreamed shortly) uses the atomicMax operation on 64-bit integers. This is only supported in compute capabilities 3.5 and later. I've changed the clang default to sm_35. Differential Revision: https://reviews.llvm.org/D40977 llvm-svn: 320082 GitOrigin-RevId: 145c54721b6e91a4fcf0d352d7e396cce3939cb1