external: import cpu_features library

Taken from https://github.com/google/cpu_features at revision
26133d3b620c2c27f31d571efd27371100f891e9

external/cpu_features/include/internal/cpuid_x86.h

@@ -0,0 +1,37 @@
+// Copyright 2017 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef CPU_FEATURES_INCLUDE_INTERNAL_CPUID_X86_H_
+#define CPU_FEATURES_INCLUDE_INTERNAL_CPUID_X86_H_
+
+#include <stdint.h>
+
+#include "cpu_features_macros.h"
+
+CPU_FEATURES_START_CPP_NAMESPACE
+
+// A struct to hold the result of a call to cpuid.
+typedef struct {
+  uint32_t eax, ebx, ecx, edx;
+} Leaf;
+
+// Retrieves the leaf for a particular cpuid.
+Leaf CpuId(uint32_t leaf_id);
+
+// Returns the eax value of the XCR0 register.
+uint32_t GetXCR0Eax(void);
+
+CPU_FEATURES_END_CPP_NAMESPACE
+
+#endif  // CPU_FEATURES_INCLUDE_INTERNAL_CPUID_X86_H_