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/time/CMakeLists.txt

@@ -0,0 +1,78 @@
+#
+# 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 TIME_PUBLIC_HEADERS
+  "clock.h"
+  "time.h"
+)
+
+
+list(APPEND TIME_INTERNAL_HEADERS
+  "internal/test_util.h"
+)
+
+list(APPEND TIME_SRC
+  "time.cc"
+  "clock.cc"
+  "duration.cc"
+  "format.cc"
+  ${TIME_PUBLIC_HEADERS}
+  ${TIME_INTERNAL_HEADERS}
+)
+set(TIME_PUBLIC_LIBRARIES absl::base absl::stacktrace absl::int128 cctz)
+
+absl_library(
+  TARGET
+    absl_time
+  SOURCES
+    ${TIME_SRC}
+  PUBLIC_LIBRARIES
+    ${TIME_PUBLIC_LIBRARIES}
+  PUBLIC_INCLUDE_DIRS
+    ${CCTZ_INCLUDE_DIRS}
+  EXPORT_NAME
+    time
+)
+
+
+
+#
+## TESTS
+#
+
+# test time_test
+list(APPEND TIME_TEST_SRC
+  "time_test.cc"
+  "clock_test.cc"
+  "duration_test.cc"
+  "format_test.cc"
+  "time_norm_test.cc"
+  "time_test.cc"
+  "time_zone_test.cc"
+  "internal/test_util.cc"
+)
+set(TIME_TEST_PUBLIC_LIBRARIES absl::time)
+
+absl_test(
+  TARGET
+    time_test
+  SOURCES
+    ${TIME_TEST_SRC}
+  PUBLIC_LIBRARIES
+    ${TIME_TEST_PUBLIC_LIBRARIES}
+)
+
+