Add branch hinting feature

[dschuff]

No description provided.

[dschuff]

@yuri91 Do you know what flags are required to enable this feature on various browser implementations?
It would be nice to add support for the proposal to https://github.com/GoogleChromeLabs/wasm-feature-detect but... I guess that will be hard because there's no validation failure that can be detected like we do for the other features. Have you had any thoughts on that?

[yuri91]

Yeah there is no way to test if the feature is implemented. but on the upside it means that people can just always include the hints section in their modules, and the module will run.

about flags:
I am not certain but I believe that JSC has no flags and just always reads the section.
for SpiderMonkey, it's --enable-wasm-branch-hinting, but i am not sure if it's on by default or not

[dschuff]

I imagine it would not be on by default if there's a flag for it (since the way browsers usually ship features is to put them behind a flag, and then flip the default from off to on... and they don't generally do that until a proposal reaches phase 4).
Maybe @eqrion could confirm about Firefox and @ddegazio about webkit.