Add support for cpp in for compute

[anthony-gomez-fastly]

Change summary

Adds ability to build C++ services and publish them

test service here

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[kpfleming]

One extraneous file, and a couple of 'nice to have' improvements. Otherwise this looks great.

[philippschulte]

Some of my findings are the same as Kevin's:

1. Please remove the committed fastly-dev binary from the repo root.
2. cpp is now exposed in compute init, but I do not see matching C++ starter-kit config. This could break the init flow if the starter-kit list is empty.
3. The new config.CPP defaults do not appear to be added to the static/generated config, so real users may get empty C++ config values.
4. WasmWasiTarget is defined but not used; either use it in the default build command or remove it for now.
5. Add an init test for --language cpp, especially covering the no-starter-kit case.

[kpfleming]

2. cpp is now exposed in compute init, but I do not see matching C++ starter-kit config. This could break the init flow if the starter-kit list is empty.

We don't have starter kits yet, that will happen next week. We do know what their URLs will be though, if those need to be included in the build.

[anthony-gomez-fastly]

@philippschulte

1. Please remove the committed fastly-dev binary from the repo root.
   Done in d5685ea
2. cpp is now exposed in compute init, but I do not see matching C++ starter-kit config. This could break the init flow if the starter-kit list is empty.
   Kevin addressed this already, I have included a test that has the starter kit URL, which fails now but should pass once we're ready and the url is public.
3. The new config.CPP defaults do not appear to be added to the static/generated config, so real users may get empty C++ config values.
   I added them to fastly.toml in c1dc0443
4. WasmWasiTarget is defined but not used; either use it in the default build command or remove it for now.
   it is used in the build process from what i understand, as demonstarted in the config.
5. Add an init test for --language cpp, especially covering the no-starter-kit case.
   done in c632e09

made changes

[kpfleming]

One very small change and this is ready to go; the tests will fail until the starter kits are made public, so we can either just accept that for a couple of weeks or skip them for now.

[philippschulte]

Thanks for the updates. Point 4 still looks unresolved to me.

I see wasm_wasi_target is now present in .fastly/config.toml and mapped onto config.CPP.WasmWasiTarget, but I do not see that value being read anywhere in the C++ build path. The default build command still hardcodes wasm32-wasip1:

var CPPDefaultBuildCommand = fmt.Sprintf("clang++ -O3 --target=wasm32-wasip1 -o %s main.cpp", binWasmPath)

and Build() assigns that constant directly when [scripts.build] is missing.

So unless I am missing another code path, WasmWasiTarget is configured but currently unused.

[anthony-gomez-fastly]

@philippschulte you're right, i missed the hardcoded value not being used, added support in 02965bcb

[philippschulte]

Thank you!