cmake-3.12.2 fails on arm

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

Hello
trying to build cmake-3.12.2 on NetBSD current earmv7hf, it fails in
configure stage with:
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Checking if compiler supports C11 _Thread_local
-- Checking if compiler supports C11 _Thread_local - yes
-- Checking if compiler supports needed C++17 constructs
-- Checking if compiler supports needed C++17 constructs - yes
-- Checking if compiler supports C++ make_unique
-- Checking if compiler supports C++ make_unique - no
-- Checking if compiler supports C++ unique_ptr
-- Checking if compiler supports C++ unique_ptr - no
CMake Error at CMakeLists.txt:92 (message):
  The C++ compiler does not support C++11 (e.g.  std::unique_ptr).

(3.12.1 did fail the same way). Does anyone have an idea how to fix this ?
Is it a misconfiguration of our gcc ?

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--