On the wasm team we build several CMake-based projects with ninja
(LLVM, binaryen, etc), and its useful for us (me at least) to be able
to use autoninja with these project too.

Change-Id: I7e213448dbbe95ffe3d249c9c6a3d4baa41f50d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1682742Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Sam Clegg <sbc@chromium.org>