swift234

[ClangImporter] Map u_int*_t [sic] to UInt*.

These types come from <sys/types.h> indirectly and show up in a few
interesting functions like arc4random_uniform.

This commit also introduces a new test file for mapping fixed-sized integers,
to eliminate boilerplate as we continue to rack up aliases for UInt*.

<rdar://problem/16978349>

Swift SVN r18505