Set @source_name for procedures with divergent source/linkage name #1351

Names in Wasm's name section need not be unique. For debug builds of examples/ with panic-abort rustc produces duplicate names in the Wasm name section, see #1341.

#1342 deduplicates names, which can lead to divergent source/linkage names. In that case, the new @source_name attribute should be added to the corresponding procedure. See vm3716 for details.

Blocked until the compiler uses vm with that feature, probably >= 0.30.