Merge pull request #18685 from nuchi/fft_no_core_framework_and_single_thread

XLA CPU Fft no core framework and single thread

diff --cc tensorflow/compiler/xla/service/cpu/BUILD
Simple merge

diff --cc tensorflow/compiler/xla/service/cpu/cpu_runtime.cc
Simple merge

diff --cc tensorflow/compiler/xla/service/cpu/cpu_runtime.h
Simple merge

diff --cc tensorflow/compiler/xla/service/cpu/ir_emitter.cc
Simple merge

diff --cc tensorflow/compiler/xla/service/cpu/simple_orc_jit.cc
Simple merge