fix 'make deps' on Windows
fix 'make deps' on Windows

Summary: windows builds use a mingw variant

Reviewed By: samwgoldman

Differential Revision: D27800717

fbshipit-source-id: 38ed26e57a6eb5e65c1ca4591ae794cdf38d2c04

mroch/flow,mroch/flow,facebook/flow,facebook/flow,mroch/flow,facebook/flow,facebook/flow,facebook/flow,facebook/flow,mroch/flow,mroch/flow,mroch/flow,mroch/flow,facebook/flow