Serialise debug strings

[vext01]

Required by ykjit/yk#1540

[ltratt]

Why "anchor"?

[vext01]

Why "anchor"?

Because we will be using these to tie/map/anchor a place in the interpreter source code to a place in the JIT IR.

I thought yk_debug() or yk_debug_msg() was too generic, since we have all kinds of other debugging facilities in place throughout the system.

[ltratt]

I admit I'm bikeshedding, but found "anchor" a bit confusing. I wondered if yk_trace_str or yk_debug_str or something might be clearer?

[vext01]

I was looking for a more specific term, but perhaps it's not worth worrying about.

If you are OK with yk_debug_str() I can use that.

[ltratt]

yk_debug_str works for me.

[vext01]

Force pushed the renaming and synced to latest master.

[vext01]

Let's hold off on this until we've fixed outlined functions that contain debug strings.

[vext01]

This is ready to merge now.