swift234

Fix latent SIL verification errors.

r15824 overrode SILVerifier::visitSILBasicBlock without calling up to the super definition, causing us to never actually verify any instructions for the past three weeks. Awesome. Patch up the latent bugs that have crept in, except for three devirtualizer tests that fail. This doesn't reenable the verifier because I don't want to cause crashes until all the regressions have been cleared up.

Swift SVN r17121