Failure building on OSX

[dabonnie]

Description

Unable to build libstatistic_collector on OSX.

Expected Behavior

OSX build passes

Actual Behavior

Found when running CI via ros2/rclcpp#1050

--- stderr: libstatistics_collector
10:51:27 /Users/osrf/jenkins-agent/workspace/ci_osx/ws/src/system_metrics_collector/libstatistics_collector/test/moving_average_statistics/test_moving_average_statistics.cpp:30:51: error: constexpr variable cannot have non-literal type 'const std::array<double, kExpectedSize>'
10:51:27 constexpr const std::array<double, kExpectedSize> kTestData{-3.5, -2.1, -1.1, 0.0, 4.7, 5.0,
10:51:27                                                   ^
10:51:27 /Users/osrf/jenkins-agent/workspace/ci_osx/ws/src/system_metrics_collector/libstatistics_collector/test/moving_average_statistics/test_moving_average_statistics.cpp:30:51: error: implicit instantiation of undefined template 'std::__1::array<double, 9>'
10:51:27 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/__tuple:223:64: note: template is declared here
10:51:27 template <class _Tp, size_t _Size> struct _LIBCPP_TEMPLATE_VIS array;
10:51:27                                                                ^
10:51:27 2 errors generated.
10:51:27 make[2]: *** [CMakeFiles/test_moving_average_statistics.dir/test/moving_average_statistics/test_moving_average_statistics.cpp.o] Error 1
10:51:27 make[1]: *** [CMakeFiles/test_moving_average_statistics.dir/all] Error 2
10:51:27 make[1]: *** Waiting for unfinished jobs....
10:51:27 make: *** [all] Error 2
10:51:27 ---
10:51:27 Failed   <<< libstatistics_collector	[ Exited with code 2 ]

https://ci.ros2.org/job/ci_osx/8133/console#console-section-5

To Reproduce

PROMPT: Steps to reproduce the behavior:

1. Start a CI job for the libstatistic_collector on OSX

System (please complete the following information)

• OS: CI OSX
• ROS2 Distro: master

[emersonknapp]

Reviewed at Sprint #17 review