This is a working solution for generating a separate Emscripten cache.
Note that this requires an additional entry in the workspace as follows:
```starlark
load("@emsdk//:emscripten_cache.bzl", emsdk_emscripten_cache = "emscripten_cache")
emsdk_emscripten_cache()
```
When used like this, the default Emscripten cache will be used. However,
if the entry is as follows:
```starlark
load("@emsdk//:emscripten_cache.bzl", emsdk_emscripten_cache = "emscripten_cache")
emsdk_emscripten_cache(flags = ["--lto"])
```
Then embuilder will be called to build all system libraries and ports
(i.e., the `ALL` option to embuilder) with the LTO option enabled. This
can take awhile, so I have also made possible to specify which libraries
you want to build explicitly:
```starlark
load("@emsdk//:emscripten_cache.bzl", emsdk_emscripten_cache = "emscripten_cache")
emsdk_emscripten_cache(
flags = ["--lto"],
libraries = [
"crtbegin",
"libprintf_long_double-debug",
"libstubs-debug",
"libnoexit",
"libc-debug",
"libdlmalloc",
"libcompiler_rt",
"libc++-noexcept",
"libc++abi-debug-noexcept",
"libsockets"
]
)
```
Resolves#807, resolves#971, resolves#1099, resolves#1362, resolves
#1401
This script is (IMO) more readable, but the real reason for this change is that
it raises an error message when the binary package fails to download. (The shell
script silently generated a bogus hash instead, because the shell's `set -e`
builtin does not affect commands executing inside a $() context.
It seemed just as easy to rewrite the script in Python as to fix that.
This change also updates some outdated filename references.
* Makes provided bazel rules look up @emsdk workspace instead of local workspace
* Uses system-specific emscripten binaries instead of defaulting to linux
* Provides macros for loading emsdk dependencies (nodejs and emscripten binaries)
* Unhardcodes paths in bazel rules and .sh wrappers
* `update_bazel_workspace.sh` now updates `revisions.bzl`
* `emscripten_deps()` can be fed with specific emscripten version
* Adds external usage test
Addresses #650 and #696
