Fix WinRT build break. angle_common needs the WinRT flags. Change-Id: I409527becc9d8d2d91766a4cc5a24f96fd2b7505 Reviewed-on: https://chromium-review.googlesource.com/241070 Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Austin Kinross <aukinros@microsoft.com>