update llvm to 615644763ffc (#7504)

* Fixes some build issues in clang headers that have changed upstream
* Adds patch 0011 to work around an upstream commit that broke Bazel
builds

toolchain/check/cpp/call.cpp

@@ -310,7 +310,7 @@ static auto BuildTemplateId(Context& context, SemIR::LocId loc_id,
           dyn_cast<clang::VarTemplateDecl>(template_decl)) {
     auto decl_result = context.clang_sema().CheckVarTemplateId(
         var_template_decl, /*TemplateLoc=*/clang::SourceLocation(), loc,
-        arg_list);
+        arg_list, /*SetWrittenArgs=*/false);
     return decl_result.isInvalid()
                ? SemIR::ErrorInst::InstId
                : ImportCppDecl(context, loc_id,

toolchain/check/cpp/export.cpp

@@ -864,11 +864,10 @@ auto ExportFunctionSpecializationToCpp(
   auto* template_arg_list = clang::TemplateArgumentList::CreateCopy(
       context.ast_context(), template_args);
   function_decl->setFunctionTemplateSpecialization(
-      context.ast_context(), function_template_decl, template_arg_list,
+      function_template_decl, template_arg_list,
       /*InsertPos=*/nullptr, clang::TSK_ExplicitSpecialization,
-      /*TemplateParams=*/nullptr, /*TemplateArgsAsWritten=*/nullptr,
-      /*PointOfInstantiation=*/clang::SourceLocation(),
-      /*AddSpecialization=*/true);
+      /*TemplateArgsAsWritten=*/nullptr,
+      /*PointOfInstantiation=*/clang::SourceLocation());
 
   return true;
 }