Right now, most paths that c2rust transpile generates are fully-qualified, like libc::c_int. This can be ambiguous, however, when there is another item named libc, which would shadow the libc crate. To fix this, we should make the qualified paths global, i.e., prefix them with a :: like ::libc::c_int, which causes the lookup to be only within crates, not within all in-scope items, which is what we want.

This can cause practical issues, like in the tests/longdouble test. When I added a typedef long double f128 to the C code, then the generated Rust code included a pub type f128 = f128::f128. That is, the f128 type alias clashed with the f128 crate. If pub type f128 = ::f128::f128 was generated, it would work.