[Type checker] Don't check near-miss candidates of the wrong kind.

Fixes rdar://problem/35832679.

(cherry picked from commit 6eec137)

Author: DougGregor

lib/Sema/TypeCheckProtocol.cpp

@@ -6479,6 +6479,11 @@ static bool shouldWarnAboutPotentialWitness(
   if (groupChecker.isCoveredMember(witness))
     return false;
 
+  // If the kinds of the requirement and witness are different, there's
+  // nothing to warn about.
+  if (req->getKind() != witness->getKind())
+    return false;
+
   // If the warning couldn't be suppressed, don't warn.
   if (!canSuppressPotentialWitnessWarningWithMovement(req, witness) &&
       !canSuppressPotentialWitnessWarningWithNonObjC(req, witness))

validation-test/compiler_crashers_2_fixed/0133-rdar35832679.swift

@@ -0,0 +1,8 @@
+// RUN: %target-swift-frontend %s -emit-ir -o -
+
+func f() {
+  enum NotAnError: Swift.Error {
+    case nope(length: Int)
+  }
+}
+