New code layout - breaking change in cpu_features_macros.h (#194)

This commit helps with platform code separation (fixes #3). It should also help with the build as we can simply include all `impl_*.c` files regardless of OS / arch.

Note: this patch contains breaking changes in `include/cpu_features_macros.h`
 - `CPU_FEATURES_OS_LINUX_OR_ANDROID` does not exist anymore
 - `CPU_FEATURES_OS_FREEBSD`, `CPU_FEATURES_OS_ANDROID` and `CPU_FEATURES_OS_LINUX` are now mutually exclusive (i.e. `CPU_FEATURES_OS_ANDROID` does not imply `CPU_FEATURES_OS_LINUX`)
 - `CPU_FEATURES_OS_DARWIN` has been renamed into `CPU_FEATURES_OS_MACOS` to be able to target non-Mac Apple products (IOS, TV, WATCH). They are now targetable with `CPU_FEATURES_OS_IPHONE`. This matches Apple naming convention described in [this stackoverflow](https://stackoverflow.com/a/49560690).

src/define_introspection.inl

@@ -0,0 +1,84 @@
+// Copyright 2017 Google LLC
+//
+// 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 INTROSPECTION_PREFIX
+#error "missing INTROSPECTION_PREFIX"
+#endif
+#ifndef INTROSPECTION_ENUM_PREFIX
+#error "missing INTROSPECTION_ENUM_PREFIX"
+#endif
+#ifndef INTROSPECTION_TABLE
+#error "missing INTROSPECTION_TABLE"
+#endif
+
+#include <stdbool.h>
+
+#define STRINGIZE_(s) #s
+#define STRINGIZE(s) STRINGIZE_(s)
+
+#define FEAT_TYPE_NAME__(X) X##Features
+#define FEAT_TYPE_NAME_(X) FEAT_TYPE_NAME__(X)
+#define FEAT_TYPE_NAME FEAT_TYPE_NAME_(INTROSPECTION_PREFIX)
+
+#define FEAT_ENUM_NAME__(X) X##FeaturesEnum
+#define FEAT_ENUM_NAME_(X) FEAT_ENUM_NAME__(X)
+#define FEAT_ENUM_NAME FEAT_ENUM_NAME_(INTROSPECTION_PREFIX)
+
+#define GET_FEAT_ENUM_VALUE__(X) Get##X##FeaturesEnumValue
+#define GET_FEAT_ENUM_VALUE_(X) GET_FEAT_ENUM_VALUE__(X)
+#define GET_FEAT_ENUM_VALUE GET_FEAT_ENUM_VALUE_(INTROSPECTION_PREFIX)
+
+#define GET_FEAT_ENUM_NAME__(X) Get##X##FeaturesEnumName
+#define GET_FEAT_ENUM_NAME_(X) GET_FEAT_ENUM_NAME__(X)
+#define GET_FEAT_ENUM_NAME GET_FEAT_ENUM_NAME_(INTROSPECTION_PREFIX)
+
+#define FEAT_ENUM_LAST__(X) X##_LAST_
+#define FEAT_ENUM_LAST_(X) FEAT_ENUM_LAST__(X)
+#define FEAT_ENUM_LAST FEAT_ENUM_LAST_(INTROSPECTION_ENUM_PREFIX)
+
+// Generate individual getters and setters.
+#define LINE(ENUM, NAME, A, B, C)                         \
+  void set_##ENUM(FEAT_TYPE_NAME* features, bool value) { \
+    features->NAME = value;                               \
+  }                                                       \
+  int get_##ENUM(const FEAT_TYPE_NAME* features) { return features->NAME; }
+INTROSPECTION_TABLE
+#undef LINE
+
+// Generate getters table
+#define LINE(ENUM, NAME, A, B, C) [ENUM] = get_##ENUM,
+static int (*const kGetters[])(const FEAT_TYPE_NAME*) = {INTROSPECTION_TABLE};
+#undef LINE
+
+// Generate setters table
+#define LINE(ENUM, NAME, A, B, C) [ENUM] = set_##ENUM,
+static void (*const kSetters[])(FEAT_TYPE_NAME*, bool) = {INTROSPECTION_TABLE};
+#undef LINE
+
+// Implements the `GetXXXFeaturesEnumValue` API.
+int GET_FEAT_ENUM_VALUE(const FEAT_TYPE_NAME* features, FEAT_ENUM_NAME value) {
+  if (value >= FEAT_ENUM_LAST) return false;
+  return kGetters[value](features);
+}
+
+// Generate feature name table.
+#define LINE(ENUM, NAME, A, B, C) [ENUM] = STRINGIZE(NAME),
+static const char* kFeatureNames[] = {INTROSPECTION_TABLE};
+#undef LINE
+
+// Implements the `GetXXXFeaturesEnumName` API.
+const char* GET_FEAT_ENUM_NAME(FEAT_ENUM_NAME value) {
+  if (value >= FEAT_ENUM_LAST) return "unknown_feature";
+  return kFeatureNames[value];
+}