Skip platform-dependent intermediate typedefs

[kkysen]

See #1266 (comment).

As a follow-up to #1266, it'd be better to also emit platform-independent intermediate typedefs. #1266 makes the final typedefs, e.x. uint32_t point to the same underlying u32, but they go through different intermediate typedefs on different platforms. This likely needs some hardcoding for things like __uint32_t on Linux or __darwin_size_t on macOS.

[fw-immunant]

It's worth noting that we do not want to collapse all intermediate typedefs, as these provide an important opportunity for post-translation refactorings; for example a codebase may typedef my_lib_size_t my_lib_array_idx_t; and typedef size_t my_lib_size_t;, and a user may want to avoid collapsing these notions. But it is likely that users are not interested in the details of their platform's implementation of standard types like uint32_t or size_t.