ClangImporter: don't import clang SPI attributes by default

include/swift/Basic/LangOptions.h

@@ -740,6 +740,9 @@ namespace swift {
     /// When set, don't look for or load overlays.
     bool DisableOverlayModules = false;
 
+    /// When set, import SPI_AVAILABLE symbols with Swift SPI attribtues.
+    bool EnableClangSPI = false;
+
     /// When set, don't enforce warnings with -Werror.
     bool DebuggerSupport = false;
 
@@ -767,7 +770,8 @@ namespace swift {
                           DetailedPreprocessingRecord,
                           ImportForwardDeclarations,
                           DisableSwiftBridgeAttr,
-                          DisableOverlayModules);
+                          DisableOverlayModules,
+                          EnableClangSPI);
     }
   };