nghttp2 broken

[Stephen Borrill <netbsd%precedence.co.uk@localhost>]

www/nghttp2 does not build on netbsd-7:

checking dependency style of gcc... gcc3
checking whether make supports nested variables... (cached) yes
checking for x86_64--netbsd-gcc... (cached) gcc
checking whether we are using the GNU C compiler... (cached) yes
checking whether gcc accepts -g... (cached) yes
checking for gcc option to accept ISO C89... (cached) none needed
checking whether gcc understands -c and -o together... (cached) yes
checking whether we are using the GNU C++ compiler... no
checking whether c++ accepts -g... no
checking how to run the C++ preprocessor... /lib/cpp
configure: error: in `/pkg_comp/obj/pkgsrc/www/nghttp2/default/nghttp2-1.35.1':
configure: error: C++ preprocessor "/lib/cpp" fails sanity check

config.log shows:
configure:13808: checking whether we are using the GNU C++ compiler
configure:13827: c++ -c -O2 -D_FORTIFY_SOURCE=2 -I/usr/include -I/usr/pkg/include -I/usr/include -I/usr/pkg/include conftest.cpp >&5
g++: error: unrecognized command line option '-std=c++14'

I assume this is triggering the fallback to /lib/cpp

Its Makefile includes:
USE_LANGUAGES=          c c++14

--
Stephen