Use external gyp

[lucab]

The latest libuv master has gained a new dependency on gyp in order to generate its Makefile. We are currently git-cloning it at build time in order to have it.

It would be good to have a switch to just use a system-wide gyp.

PS. note that this is also means that next stable source tarball is going to have dependency on git. Maybe it would be better to use a git submodule also for gyp?

[huonw]

Doesn't the source tarball already depend on git for LLVM & libuv? (I could easily be wrong; I have no idea about this.)

[lucab]

The submodules are fetched by make dist and bundled in the tar.gz. The idea is that (if you want/need) you don't have to rely on external resources or even the network to build from the tar archive. This also helps improving deterministic builds.

[alexcrichton]

I agree that when we re-update libuv (reverting the revert), that a submodule is the best way to go here.