While doing so, we:
* keep the latest activation (e.g., the user may have activated latest and then latest-upstream, then the upstream LLVM is what is desired).
* keep the order of keys fixed (so the relative order of lines in the .emscripten file is fixed)
This adds some assertions in the Dockerfile, to verify we have one LLVM_ROOT command, and it is the right one.
Fixes#194
(This was reverted by mistake. It had a bad commit message though, so relanding with a nicer one is nice anyhow.)
With this, we can do emsdk install latest-fastcomp and it installs fastcomp from the waterfall. That is, we then have 3 main sdks people might want to use:
* latest which installs fastcomp-llvm (plus emscripten etc.) from the mozilla infrastructure. (fetches the last emscripten version there)
* latest-upstream which installs upstream-llvm (plus emscripten etc.) from the waterfall infrastructure. (fetches the last known good revision (lkgr) there)
* latest-fastcomp which installs fastcomp-llvm (plus emscripten etc.) from the waterfall infrastructure. (fetches the last known good revision (lkgr) there)
The first and last are currently somewhat overlapping in that both fetch a build of fastcomp. However, as we transition away from the mozilla infrastructure, we could just make latest an alias for latest-fastcomp. (And later, when we're ready to switch to the wasm backend by default, the alias could switch to latest-upstream.)
This makes it possible to tell the emsdk to get "latest-upstream", which fetches the latest lkgr from there. This will probably be a common use pattern, I expect we may want to recommend users start trying out the wasm backend that way soon. This will also let us simplify this code: https://github.com/kripken/emscripten/blob/incoming/.circleci/config.yml#L334
Aside from adding the "latest-upstream" alias, this PR has
* A few minor cleanups in the emsdk code.
( Minor restructuring of how we define the upstream stuff in the manifest: It seemed odd to have 3 things (clang, emscripten, binaryen) that are all coming from a single archive from the waterfall. Simpler to have just one - the archive is one big lump, there's no way to download just part of it.
* Also add node 8.9.1 as a dependency of the upstream sdk, which makes things usable out of the box (node.js is the one thing not provided by the waterfall archive).
