skip attribute: make them work on non-inline mod

[W95Psp]

cc @franziskuskiefer

Status

We have now an include attribute and an exclude attribute.

Due to rust-lang/rust#54727, on stable, a proc macro cannot work on non-inline modules (an inline module is mod foo { ... items ... }, whereas a non-inline module is ie mod foo; with foo.rs is a file).

Our hax attributes are working with two layers: we have some proc-macros that get transformed into tool attributes but only when compiling via hax, because tool attributes are nightly.

Technically, until either tool attributes or rust-lang/rust#54727 are nightly, I don't think we can solve this issue. But, since we now support the -i flag in the cargo hax into command line, maybe this issue is not important any longer.