Bug 1501129 - Use field names instead of their index when mangling. r=mccr8

Differential Revision: https://phabricator.services.mozilla.com/D9558

--HG--
extra : moz-landing-system : lando

build/clang-plugin/mozsearch-plugin/MozsearchIndexer.cpp

@@ -398,7 +398,7 @@ private:
     } else if (const FieldDecl *D2 = dyn_cast<FieldDecl>(Decl)) {
       const RecordDecl *Record = D2->getParent();
       return std::string("F_<") + getMangledName(Ctx, Record) + ">_" +
-             toString(D2->getFieldIndex());
+             D2->getNameAsString();
     } else if (const EnumConstantDecl *D2 = dyn_cast<EnumConstantDecl>(Decl)) {
       const DeclContext *DC = Decl->getDeclContext();
       if (const NamedDecl *Named = dyn_cast<NamedDecl>(DC)) {