Add more constness to module-related APIs

llvm-svn: 206595
diff --git a/clang/lib/Basic/Module.cpp b/clang/lib/Basic/Module.cpp
index 2612ee0..d5c02d8 100644
--- a/clang/lib/Basic/Module.cpp
+++ b/clang/lib/Basic/Module.cpp
@@ -91,7 +91,7 @@
   llvm_unreachable("could not find a reason why module is unavailable");
 }
 
-bool Module::isSubModuleOf(Module *Other) const {
+bool Module::isSubModuleOf(const Module *Other) const {
   const Module *This = this;
   do {
     if (This == Other)