Revert "Turn on ‘as’ bridging on Linux."

lib/Sema/CSSimplify.cpp

@@ -3627,6 +3627,11 @@ ConstraintSystem::simplifyBridgingConstraint(Type type1,
                                              Type type2,
                                              TypeMatchOptions flags,
                                              ConstraintLocatorBuilder locator) {
+  // There's no bridging without ObjC interop, so we shouldn't have set up
+  // bridging constraints without it.
+  assert(TC.Context.LangOpts.EnableObjCInterop
+         && "bridging constraint w/o ObjC interop?!");
+  
   TypeMatchOptions subflags = getDefaultDecompositionOptions(flags);
 
   /// Form an unresolved result.
@@ -5071,11 +5076,14 @@ void ConstraintSystem::addExplicitConversionConstraint(
   coerceConstraint->setFavored();
   constraints.push_back(coerceConstraint);
 
-  // The source type can be explicitly converted to the destination type.
-  Constraint *bridgingConstraint =
-  Constraint::create(*this, ConstraintKind::BridgingConversion,
-                     fromType, toType, locatorPtr);
-  constraints.push_back(bridgingConstraint);
+  // Bridging.
+  if (getASTContext().LangOpts.EnableObjCInterop) {
+    // The source type can be explicitly converted to the destination type.
+    Constraint *bridgingConstraint =
+      Constraint::create(*this, ConstraintKind::BridgingConversion,
+                         fromType, toType, locatorPtr);
+    constraints.push_back(bridgingConstraint);
+  }
 
   if (allowFixes && shouldAttemptFixes()) {
     Constraint *downcastConstraint =
@@ -5086,8 +5094,8 @@ void ConstraintSystem::addExplicitConversionConstraint(
   }
 
   addDisjunctionConstraint(constraints, locator,
-                           allowFixes ? RememberChoice
-                                      : ForgetChoice);
+    getASTContext().LangOpts.EnableObjCInterop && allowFixes ? RememberChoice
+                                                             : ForgetChoice);
 }
 
 ConstraintSystem::SolutionKind