Accept `@cdecl` enums without an explicit C name. The C name defaults to
the Swift one. It is printed using the `SWIFT_ENUM` macro instead of
`SWIFT_ENUM_NAMED`.
Begin accepting the attribute in the form of `@cdecl(cName)`, using an
identifier instead of a string.
For ease of landing this change we still accept the string form. We
should stop accepting it before making this feature available in
production.
Print @cdecl enums in the C section of the compatibility header. Use and
extend the macros to support C compiler clients.
The macro is adapted to the features supported by the client compiler.
It uses an Objective-C style macro with raw type when available and
fallbacks to a simple typedef for C compatibility.
Add a block for C clients in the compatibility header. This block
contains only the `@cdecl` functions that are printed using only C
types.
This C block is printed above the Objective-C and C++ blocks as if we
add support for `@cdecl` types other languages should be able to
reference them in function signatures. Other languages block don't
duplicate printing the `@cdecl` functions either as they are already
accessible to them.
