Should it work with /configure '--with-cxx-main=g++' && make?

Because currently it doesn't:

g++ -c -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes    -Werror=declaration-after-statement   -I. -IInclude -I./Include    -DPy_BUILD_CORE -o Programs/python.o ./Programs/python.c
cc1plus: warning: command line option ‘-Wstrict-prototypes’ is valid for C/ObjC but not for C++
In file included from Include/pyatomic.h:10:0,
                 from Include/Python.h:53,
                 from ./Programs/python.c:3:
/usr/lib64/gcc/x86_64-pld-linux/5.2.0/include/stdatomic.h:40:9: error: ‘_Atomic’ does not name a type
[...]

(testing 3.5.0 + patch for this issue from hg)