swift234

Prohibit type declarations within generic functions, which were causing the compiler to crash.

You'll notice that we already had tests that made it appear that such declarations could work,
but they were only avoiding crashes because downstream errors were already marking the
enclosing functions as invalid. (If the errors were fixed, they would also crash the compiler.)

This addresses crash suite scenario 018. (rdar://problem/18299547)

Swift SVN r22109