Sema: Define {Abstract,Inferred}GenericSignatureRequest::isCached() inside the request type

Author: slavapestov

include/swift/AST/TypeCheckRequests.h

@@ -1414,7 +1414,7 @@ class AbstractGenericSignatureRequest :
 
 public:
   // Separate caching.
-  bool isCached() const;
+  bool isCached() const { return true; }
 
   /// Abstract generic signature requests never have source-location info.
   SourceLoc getNearestLoc() const {
@@ -1449,7 +1449,7 @@ class InferredGenericSignatureRequest :
 
 public:
   // Separate caching.
-  bool isCached() const;
+  bool isCached() const { return true; }
 
   /// Inferred generic signature requests don't have source-location info.
   SourceLoc getNearestLoc() const {

lib/AST/GenericSignatureBuilder.cpp

@@ -8738,14 +8738,6 @@ void GenericSignatureBuilder::verifyGenericSignaturesInModule(
     verifyGenericSignature(context, canGenericSig);
   }
 }
-
-bool AbstractGenericSignatureRequest::isCached() const {
-  return true;
-}
-
-bool InferredGenericSignatureRequest::isCached() const {
-  return true;
-}
 
 /// Check whether the inputs to the \c AbstractGenericSignatureRequest are
 /// all canonical.