oglcts-runner: Include cstdlib in glcTestRunnerMain

oglcts-runner: Include cstdlib in glcTestRunnerMain

To pick up the definitions of EXIT_SUCCESS/EXIT_FAILURE.

Fixes these errors building on FreeBSD 10.4 with llvm60:
/root/nvt/tests/buildvulkancts/vk-gl-cts/external/openglcts/modules/runner/glcTestRunnerMain.cpp:115:19: error: use of undeclared identifier 'EXIT_SUCCESS'
        int exitStatus = EXIT_SUCCESS;
                         ^
/root/nvt/tests/buildvulkancts/vk-gl-cts/external/openglcts/modules/runner/glcTestRunnerMain.cpp:136:19: error: use of undeclared identifier 'EXIT_FAILURE'
                                        exitStatus = EXIT_FAILURE;
                                                     ^

Components: OpenGL

VK-GL-CTS issue: 2696

Change-Id: I918f3de12dde8871df8905f5870c3d6c73ae8048