swift234

Don't stop typechecking stmts on failure.

Generally speaking, it's necessary to typecheck all parts of a
statement regardless of whether earlier parts failed to typecheck. For
example, even if the condition of an if-statement fails to typecheck, we
should still check its branches. This way all expressions in the AST are
processed (i.e. SequenceExprs translated to trees) and we get more
diagnostics.

The big thing left to fix is for-each statement checking. If there are
any type errors in the pattern or sequence of a for-each statement, the
body doesn't get type-checked.

<rdar://problem/23684220>