Handle tmp dir on Android
Handle tmp dir on Android

Summary:
There is no universally accessible tmpdir on Android which
means mkstemp fails. This diff calls a function that the test runner
should provide to fill a valid temporary directory.

Reviewed By: yangchi

Differential Revision: D2842034

fb-gh-sync-id: 186c931ddf4424cb482c8fbd728ae37877017685

facebook/wangle,facebook/wangle,facebook/wangle,Dalzhim/wangle,Dalzhim/wangle