[libvirt] [PATCH] build: ask for -std=gnu99 explicitly

[Peter Krempa]

On Mon, Oct 07, 2019 at 15:09:52 +0100, Daniel Berrange wrote:
> We previously got -std=gnu99 secretly enabled as a side-effect
> of requesting the 'stdarg' gnulib module. We rely on some
> extensions from c99/gnu99 and while RHEL-7 supports this, it
> still defaults to gnu89.  RHEL-7 also supports some newer
> standards but declares them experimental/incomplete, so sticking
> with gnu99 is best bet for now & matches historical usage.
> 
> Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
> ---
>  m4/virt-compile-warnings.m4 | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/m4/virt-compile-warnings.m4 b/m4/virt-compile-warnings.m4
> index f9460e82ba..502f7384ff 100644
> --- a/m4/virt-compile-warnings.m4
> +++ b/m4/virt-compile-warnings.m4
> @@ -189,6 +189,10 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
>        wantwarn="$wantwarn -Werror"
>      fi
>  
> +    # Request the gnu99 standard which is the best choice with
> +    # gcc 4.8.0
> +    wantwarn="-std=gnu99"
> +

It feels odd to add this via the warning flags variable.

I know this is a hack until we get rid of the old build system, but I
think you should at least admit it in the commit message or comment that
it's deliberate.