[OPENMP5.0]Add support for device_type clause in declare target

[OPENMP5.0]Add support for device_type clause in declare target
construct.

OpenMP 5.0 introduced new clause for declare target directive, device_type clause, which may accept values host, nohost, and any. Host means
that the function must be emitted only for the host, nohost - only for
the device, and any - for both, device and the host.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@369775 91177308-0d34-0410-b5e6-96231b3b80d8