[silgen] Verify protocol witnesses's SIL right after emitting them.

These still get verified as part of SILGenModule's verification during
SILGenModule's destructor. But moving this earlier catches the error earlier and
makes it easier to debug any SIL issues immediately in the debugger rather than
having to backtrack from the SILGenModule's destructor.

Author: gottesmm

lib/SILGen/SILGenPoly.cpp

@@ -4617,4 +4617,7 @@ void SILGenFunction::emitProtocolWitness(
   formalEvalScope.pop();
   scope.pop();
   B.createReturn(loc, reqtResultValue);
+
+  // Now that we have finished emitting the function, verify it!
+  F.verify();
 }