Enable wasm pointer tracking for gc=none.

[anuraaga]

Fixes #3278

This takes the simpler approach of allowing wasm pointer tracking on the stack to be enabled even with gc=none. none is documented as being useful for combining with a separate garbage collector. However in practice, it is basically impossible to do this with wasm because tracking pointers on the stack is required for any GC to be able to see them to mark them.

It seems reasonable to enable the stack tracking code even when not using the TinyGo GC. Either a) an external GC is being used and the tracking is required or b) an external GC is not being used meaning there are no allocations, and therefore no tracking will actually happen.

Having the ability to swap in a custom GC allows TinyGo compiled wasm to perform quite well with low pause times, so this is very enabling for projects like coraza-proxy-wasm

[dgryski]

LGTM. Seems safe enough.

[deadprogram]

Thank you for the addition @anuraaga and to @dgryski for reviewing. Now merging.

[aykevl]

I don't think we should do this, to be honest. There are many things needed to integrate a GC, and -gc=none is not really able to capture it all. The -gc=none flag was mostly intended for debugging and to make sure binaries have the smallest possible code size. Enabling pointer tracking defeats this purpose.

[deadprogram]

Hmm, perhaps I merged too quickly then. 😿

[aykevl]

On the other hand, while I'm not entirely sold on -gc=custom yet, if we are going to support custom GCs then using -gc=custom is in my opinion the correct way to do so.