swift234

ClangImporter: import size_t as Int

Converging APIs to use ``Int`` as the default integer type allows users to
write fewer explicit type conversions.

Importing ``size_t`` as a signed ``Int`` type is not be a problem for 64-bit
platforms.  32-bit platforms are important, but the usecase for an
unsigned ``size_t`` on 32-bit platforms is pretty marginal, and for code
that nevertheless needs to do that there is always the option of doing a
bitcast to ``UInt`` or using C.

rdar://18949559

Swift SVN r25070