swift234

SIL Verifier: Verify that vtable entries match the ABI of their base.

This exposes a problem with the sil_vtable parser, that it can't differentiate overloads (rdar://problem/19572342), and breaks a test that exposes the fact we don't reabstract overrides that have a less abstract native calling convention than their base (rdar://problem/19572664).

Swift SVN r24667