AST: Lazily compute conditional requirements in conditional conformance

In one test where we used to dump conditional requirements we now print
a message that they have not been computed yet. I couldn't come up with
a way to force them to be computed here, but for the most part this test
is just ensuring that we don't recurse forever when printing recursive
conformances.

Author: slavapestov

include/swift/AST/ProtocolConformance.h

@@ -415,7 +415,6 @@ class NormalProtocolConformance : public ProtocolConformance,
   {
     assert(!conformingType->hasArchetype() &&
            "ProtocolConformances should store interface types");
-    differenceAndStoreConditionalRequirements();
   }
 
   NormalProtocolConformance(Type conformingType,
@@ -428,7 +427,6 @@ class NormalProtocolConformance : public ProtocolConformance,
   {
     assert(!conformingType->hasArchetype() &&
            "ProtocolConformances should store interface types");
-    differenceAndStoreConditionalRequirements();
   }
 
   void resolveLazyInfo() const;

lib/AST/ProtocolConformance.cpp

@@ -886,7 +886,6 @@ SpecializedProtocolConformance::SpecializedProtocolConformance(
     GenericSubstitutions(substitutions)
 {
   assert(genericConformance->getKind() != ProtocolConformanceKind::Specialized);
-  computeConditionalRequirements();
 }
 
 void SpecializedProtocolConformance::computeConditionalRequirements() const {

test/Frontend/debug-generic-signatures.swift

@@ -118,8 +118,7 @@ extension Super: P2 where T: P2, U: P2 {
 // CHECK-NEXT:              (normal_conformance type=Recur protocol=P2 (details printed above))))
 // CHECK-NEXT:         (conformance type=U
 // CHECK-NEXT:            (normal_conformance type=Recur protocol=P2 (details printed above))))
-// CHECK-NEXT:     conforms_to: NonRecur P2
-// CHECK-NEXT:     conforms_to: Recur P2
+// CHECK-NEXT:     (conditional requirements unable to be computed)
 // CHECK-NEXT:     (normal_conformance type=Super<T, U> protocol=P2
 // CHECK-NEXT:       (assoc_type req=A type=T)
 // CHECK-NEXT:       (assoc_type req=B type=T)