const'ify an API's parameters. NFC

Author: DougGregor

include/swift/ClangImporter/ClangImporter.h

@@ -323,8 +323,8 @@ ImportDecl *createImportDecl(ASTContext &Ctx, DeclContext *DC, ClangNode ClangN,
 ///
 /// This routine is used for various hacks that are only permitted within
 /// overlays of imported modules, e.g., Objective-C bridging conformances.
-bool isInOverlayModuleForImportedModule(DeclContext *overlayDC,
-                                        DeclContext *importedDC);
+bool isInOverlayModuleForImportedModule(const DeclContext *overlayDC,
+                                        const DeclContext *importedDC);
 
 } // end namespace swift
 

lib/ClangImporter/ClangImporter.cpp

@@ -3324,8 +3324,8 @@ importName(const clang::NamedDecl *D,
     getDeclName();
 }
 
-bool swift::isInOverlayModuleForImportedModule(DeclContext *overlayDC,
-                                               DeclContext *importedDC) {
+bool swift::isInOverlayModuleForImportedModule(const DeclContext *overlayDC,
+                                               const DeclContext *importedDC) {
   overlayDC = overlayDC->getModuleScopeContext();
   importedDC = importedDC->getModuleScopeContext();