Use DW_AT_segment for multi-memory ?

[yurydelendik]

Extend DW_OP_Wasm_location to point variables (e.g. DW_TAG_variable) to proper memory. The DW_AT_segment has type of "exprloc", so we can use DW_OP_Wasm_location or other vendor tag to point to right memory, e.g. wasm-memory 2 as segment which points to third wasm memory.

Notice that attaching DW_AT_segment to the CU extends it to the entire unit including code range -- it might be a good or bad thing.

See also https://github.com/WebAssembly/multi-memory/

[yurydelendik]

After digging more about DW_AT_segment -- it comes from i386 architecture where actual physical address is computed based on segment and offset, and that gives address in single address space. We need more.

Looks like DW_OP_xderef-family of operators covers more and actually express what multi memory load and store do.