patchci: add job for gcc-4.8 to GitHub Actions

> unlike the other jobs; using an older ubuntu base image that provides
> that compiler as an option.
> 
> note the obsoleted travis job used an image of the OS that is EOL and
> therefore not available, but the compiler used will be the same, and
> more importantly will fail in the same (C89 compatibility) issues.
> 
> Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
> ---
> based on top of my tip for cb/reftable-fixes, but applies cleanly all
> the way to maint.
> 
> a succesful run can be seen in:
> 
>   https://github.com/carenas/git/runs/3336674183
> 
> it adds 2m to the current setup, but gcc 4.8 is hard to find in modern
> developer workstations (or even non EOL enterprise systems)

> diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
> index 73856bafc9..0f211173fc 100644
> --- a/.github/workflows/main.yml
> +++ b/.github/workflows/main.yml
> @@ -297,6 +297,9 @@ jobs:
>            - jobname: linux-gcc-default
>              cc: gcc
>              pool: ubuntu-latest
> +          - jobname: linux-gcc-4.8
> +            cc: gcc-4.8
> +            pool: ubuntu-18.04

>      env:
>        CC: ${{matrix.vector.cc}}
>        jobname: ${{matrix.vector.jobname}}
> diff --git a/ci/install-dependencies.sh b/ci/install-dependencies.sh
> index 67852d0d37..950bc39129 100755
> --- a/ci/install-dependencies.sh
> +++ b/ci/install-dependencies.sh
> @@ -72,10 +72,14 @@ Documentation)
>  	test -n "$ALREADY_HAVE_ASCIIDOCTOR" ||
>  	sudo gem install --version 1.5.8 asciidoctor
>  	;;
> -linux-gcc-default|linux-gcc-4.8)
> +linux-gcc-default)
>  	sudo apt-get -q update
>  	sudo apt-get -q -y install $UBUNTU_COMMON_PKGS
>  	;;
> +linux-gcc-4.8)
> +	sudo apt-get -q update
> +	sudo apt-get -q -y install $UBUNTU_COMMON_PKGS gcc-4.8
> +	;;

> Forgive me, I probably missed a discussion about this
> somewhere else on the list, but...
> 
> Could you describe why we want GCC 4.8 in our CI? Is that a
> compiler version that we officially support? What kind of
> syntax triggers a problem on 4.8 versus latest?

> On Mon, Aug 16, 2021 at 12:06:46PM -0400, Derrick Stolee wrote:
> 
> > Forgive me, I probably missed a discussion about this
> > somewhere else on the list, but...
> > 
> > Could you describe why we want GCC 4.8 in our CI? Is that a
> > compiler version that we officially support? What kind of
> > syntax triggers a problem on 4.8 versus latest?
> 
> Try fb9d7431cf (travis-ci: build with GCC 4.8 as well, 2019-07-18).
> (found with "git log -Sgcc-4.8 ci"). The gist of it is to find variable
> declarations in for-loops.
> 
> IMHO it may be more trouble than it's worth. If we can't find a compiler
> that complains on this construct, then maybe it is not a construct worth
> worrying too much about.

> > Try fb9d7431cf (travis-ci: build with GCC 4.8 as well, 2019-07-18).
> > (found with "git log -Sgcc-4.8 ci"). The gist of it is to find variable
> > declarations in for-loops.
> > 
> > IMHO it may be more trouble than it's worth. If we can't find a compiler
> > that complains on this construct, then maybe it is not a construct worth
> > worrying too much about.
> 
> I for one like for loop initial declarations, because they allow us to
> limit the scope of the loop variable to the loop, and would love to
> see it used in more places (well, wherever possible, actually, but
> that'd be a lot of churn).  So I would prefer to just drop this job
> sooner rather than later, update CodingGuidelines, and, if deemed
> necessary, launch a weather balloon.

> I for one like for loop initial declarations, because they allow us to
> limit the scope of the loop variable to the loop, and would love to
> see it used in more places (well, wherever possible, actually, but
> that'd be a lot of churn).  So I would prefer to just drop this job
> sooner rather than later, update CodingGuidelines, and, if deemed
> necessary, launch a weather balloon.

> On 8/16/2021 12:57 AM, Carlo Marcelo Arenas Belón wrote:
> > it adds 2m to the current setup, but gcc 4.8 is hard to find in modern
> > developer workstations (or even non EOL enterprise systems)
>
> Forgive me, I probably missed a discussion about this
> somewhere else on the list, but...
>
> Could you describe why we want GCC 4.8 in our CI? Is that a
> compiler version that we officially support?