warn when int or uint is used in a native type decl

[nikomatsakis]

Perhaps we should issue a warning---or even an error?---when int or uint is used in a native type declaration? It is a very common mistake to assume they are the same as the C types int and unsigned. We could suggest the use of ctypes::c_int or ctypes::long etc.

[jckarter]

You'd want to make sure the warning doesn't trigger when referring to Rust int by the ctypes::ptrint_t alias.

[nikomatsakis]

Yes, I would only trigger the warning if the user literally typed int or uint. In other words, base the warning on the ast::ty (AST), not on the ty::t (resolved type).

[lht]

Closed by commits:

f03eb96 rustc: Warn when int or uint is used in a native type decl
dde4186 Use ctypes in native function declarations
04882d7 rustc: Use integer from ctypes consistently
7b1724f libstd: Revert an integer type casting