build: check for C++ 20 and 2b
commit15ba35a51bee27c8b7d4c5ef47673de4db6528af
authorAkim Demaille <akim.demaille@gmail.com>
Thu, 12 Aug 2021 06:31:38 +0000 (12 08:31 +0200)
committerAkim Demaille <akim.demaille@gmail.com>
Thu, 12 Aug 2021 07:07:36 +0000 (12 09:07 +0200)
treec442d772351420a0591d11f8e4c0ca03ac7f46f5
parentdb66acc5d0f433a32d49eb840bd319d25b3a657f
build: check for C++ 20 and 2b

C++20 is released.

* configure.ac, m4/bison-cxx-std.m4, tests/atlocal.in,
* tests/local.at: Replace 2a with 20, and add support for 2b.
configure.ac
m4/bison-cxx-std.m4
tests/atlocal.in
tests/local.at