[SE] Host platform implementation

This implementation does not currently support multiple concurrent streams, and
it won't allow kernels to be launched with grids larger than one block or
blocks larger than one thread. These limitations could be removed in the future
by launching new threads on the host, but that is not done in this

Reviewers: jlebar

Subscribers: beanz, mgorny, jprice, parallel_libs-commits

Differential Revision: https://reviews.llvm.org/D24473

llvm-svn: 281377
GitOrigin-RevId: 3088696499c2d883d8573eb384cd5d2455a3c6c1
8 files changed