Because the shims are generally meant for the standard library build,
which requires clang, we can default to using the compiler vended
information for the types.
Unfortunately, `cl` does not support C11. Guard the `_Generic` approach and in
C++ mode use `std::make_signed`. Thanks to Jordan Rose for the reminder about
the type_traits helper!
`ssize_t` is not universally available as it is not a standard type.
However, we require clang to build the runtime due to custom calling
convention support. As a result, we know that the compiler will support
the `_Generic` keyword from the C11 standard. Use this with an
expansion to map the type appropriately for all targets. This avoids
having to have a sanity check in the runtime that the type definition
matches the underlying system.
The standard library has grown significantly, and we need a new
directory structure that clearly reflects the role of the APIs, and
allows future growth.
See stdlib/{public,internal,private}/README.txt for more information.
Swift SVN r25876
