CMake support

- initial cmake support
- downgrade cmake requirement to 2.8.12
- factorize cmake test flags / libs options
- refactor test / library under helpers functions, follow bazel's style
- Add fix for MSVC and Windows support ( thx @patrikfors )
- Switch to default "add_subdirectory()" usage mode
- add CMake/README.md for instructions
- add header-only cmake target generator
- map absl target to absl:: namespace

absl/meta/CMakeLists.txt

@@ -0,0 +1,49 @@
+#
+# Copyright 2017 The Abseil Authors.
+#
+# 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.
+#
+
+list(APPEND META_PUBLIC_HEADERS
+  "type_traits.h"
+)
+
+
+#
+## TESTS
+#
+
+# test type_traits_test
+list(APPEND TYPE_TRAITS_TEST_SRC
+  "type_traits_test.cc"
+  ${META_PUBLIC_HEADERS}
+)
+
+absl_header_library(
+  TARGET
+    absl_meta
+  EXPORT_NAME
+    meta
+ )
+
+absl_test(
+  TARGET
+    type_traits_test
+  SOURCES
+    ${TYPE_TRAITS_TEST_SRC}
+  PUBLIC_LIBRARIES
+    ${TYPE_TRAITS_TEST_PUBLIC_LIBRARIES} absl::meta
+)
+
+
+