Clang >= 19.0 requires a template argument list after the template
keyword for CWG96 compliance, see
https://github.com/llvm/llvm-project/pull/80801
Obtained from: Bernhard Rosenkränzer, via
68ced8bd5c
PR: 259331 (comment #6)
Reported by: Tamaoki Aoki
Approved by: portmgr@ (blanket approval for fixing broken builds)