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lix/m4/ax_cxx_compile_stdcxx_17.m4
Niklas Hambüchen 57daa860e8 autoconf: Fix C++17 detection not working on Ubuntu 16.04.
And probably many other distributions.

Until now, ./configure would fail silently printing a warning

    ./configure: line 4621: AX_CXX_COMPILE_STDCXX_17: command not found

and then continuing, later failing with a C++ #error saying that some C++11
feature isn't supported (it didn't even get to the C++17 features).

This is because older distributions don't come with the
`AX_CXX_COMPILE_STDCXX_17` m4 macro.

This commit vendors that macro accordingly.

Now ./configure complains correctly:

    configure: error: *** A compiler with support for C++17 language features is required.

On Ubuntu 16.04, ./configure completes if a newer compiler is used, e.g. with
gcc-7 from https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/test
using:

    ./bootstrap.sh
    ./configure CXX=g++-7 --disable-doc-gen --with-boost=$(nix-build --no-link '<nixpkgs>' -A boost.dev)
2019-07-03 04:32:25 +02:00

36 lines
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# =============================================================================
# https://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx_17.html
# =============================================================================
#
# SYNOPSIS
#
# AX_CXX_COMPILE_STDCXX_17([ext|noext], [mandatory|optional])
#
# DESCRIPTION
#
# Check for baseline language coverage in the compiler for the C++17
# standard; if necessary, add switches to CXX and CXXCPP to enable
# support.
#
# This macro is a convenience alias for calling the AX_CXX_COMPILE_STDCXX
# macro with the version set to C++17. The two optional arguments are
# forwarded literally as the second and third argument respectively.
# Please see the documentation for the AX_CXX_COMPILE_STDCXX macro for
# more information. If you want to use this macro, you also need to
# download the ax_cxx_compile_stdcxx.m4 file.
#
# LICENSE
#
# Copyright (c) 2015 Moritz Klammler <moritz@klammler.eu>
# Copyright (c) 2016 Krzesimir Nowak <qdlacz@gmail.com>
#
# Copying and distribution of this file, with or without modification, are
# permitted in any medium without royalty provided the copyright notice
# and this notice are preserved. This file is offered as-is, without any
# warranty.
#serial 2
AX_REQUIRE_DEFINED([AX_CXX_COMPILE_STDCXX])
AC_DEFUN([AX_CXX_COMPILE_STDCXX_17], [AX_CXX_COMPILE_STDCXX([17], [$1], [$2])])