AutoDiff: Synthesize the memberwise initializer earlier

We need to do this before we synthesize the body of the
AdditiveArithmetic witnesses, so that it becomes part of
the ABI members of the nominal.

Author: slavapestov

lib/Sema/DerivedConformanceAdditiveArithmetic.cpp

@@ -207,6 +207,12 @@ static ValueDecl *deriveMathOperator(DerivedConformance &derived,
   operatorDecl->copyFormalAccessFrom(nominal, /*sourceIsParentContext*/ true);
 
   derived.addMembersToConformanceContext({operatorDecl});
+
+  // For the effective memberwise initializer before we force the body,
+  // so that it becomes part of the emitted ABI members even if we don't
+  // emit the body.
+  (void) nominal->getEffectiveMemberwiseInitializer();
+
   return operatorDecl;
 }
 
@@ -311,6 +317,12 @@ static ValueDecl *deriveAdditiveArithmetic_zero(DerivedConformance &derived) {
   getterDecl->setBodySynthesizer(deriveBodyAdditiveArithmetic_zero, nullptr);
 
   derived.addMembersToConformanceContext({propDecl, pbDecl});
+
+  // For the effective memberwise initializer before we force the body,
+  // so that it becomes part of the emitted ABI members even if we don't
+  // emit the body.
+  (void) nominal->getEffectiveMemberwiseInitializer();
+
   return propDecl;
 }