GCC selftest improvements

[Pedro Alves]

On 10/29/19 8:40 AM, Richard Biener wrote:
> On Mon, Oct 28, 2019 at 10:47 PM Jakub Jelinek <jakub@redhat.com> wrote:
>>

>> As discussed earlier, we gain most through C++11 support, there is no need
>> to jump to C++17 or C++20 as requirement.
> 
> Yes, I've agreed to raise the requirement to GCC 4.8 which provides
> C++11 support.
> 
> For convenience we could also provide a configure-time hint if the host compiler
> doesn't have C++11 support or is older than 4.8.2 (I think .1 has some issues).
> Rather than only running into some obscure errors later on.

FWIW, GDB uses a slightly modified AX_CXX_COMPILE_STDCXX to check for C++11
support at configure time, and add -std=gnu++11 if the necessary, adding nothing
if the compiler supports C++11 or later OOTB (so that you can still access
C++14-or-later features&optimizations conditionally).

 https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gdb/ax_cxx_compile_stdcxx.m4

 https://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx.html

 https://sourceware.org/ml/gdb-patches/2016-10/msg00775.html

In practice, that returns "supports" for GCC 4.8 and above, which is
GDB's minimum requirement.  I'm not sure about 4.8.x patch level.

Thanks,
Pedro Alves