swift234

Add infrastructure to easily map C types to swift stdlib types when they are
binary compatible.

This enables us to import MacTypes.h types as stdlib swift types to avoid name
conflicts.  We also import stdint.h types as stdlib swift types.

We can not map 'long double'-based ctypes.Float80 to swift.Float80 because size
of long double is 128 according to SysV ABI, and I compare that against what
the type name says (I did not find a way to find the size of the type).

Darwin.Float80 is a struct, so I don’t think we can import it as swift.Float80.
So with import Darwin, Float80 is still ambiguous.

I had to rename test/ClangModules/ctypes.swift ->
test/ClangModules/ctypes_test.swift because other tests do 'import ctypes',
which picks up 'ctypes.swift'.


Swift SVN r5727