This is just to test that the PSTL works with parallelization. This is not supposed to be a production-ready backend. Reviewed By: ldionne, #libc Spies: EricWF, arichardson, libcxx-commits Differential Revision: https://reviews.llvm.org/D150284
Reviewed By: ldionne, #libc Spies: libcxx-commits Differential Revision: https://reviews.llvm.org/D149615
Reviewed By: ldionne, #libc Spies: arichardson, pcwang-thead, libcxx-commits, miyuki Differential Revision: https://reviews.llvm.org/D150277
This allows backends to customize arbitrary parallel algorithms, which was requested pretty often. Reviewed By: #libc, ldionne Spies: arichardson, miyuki, crtrott, dalg24, __simt__, philnik, libcxx-commits Differential Revision: https://reviews.llvm.org/D149686
