getdeps: add support for using ccache in cmake builds
getdeps: add support for using ccache in cmake builds

Summary:
if we find ccache in the path, then we instruct cmake to use
it as the compiler launcher.

Reviewed By: pkaush

Differential Revision: D15375441

fbshipit-source-id: 602fe54742a5ec07b0533bd2cf63cb905b051e85

facebook/wangle,facebook/wangle,facebook/wangle