[ios] Allow using ipc on iOS via GN.
[ios] Allow using ipc on iOS via GN.

GYP supports ipc for iOS. IPC is used in Mojo and iOS will support Mojo
for WebUI.

BUG=611843

Review-Url: https://codereview.chromium.org/1976263003
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#393651}

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