gh-35810: Drop support for GCC < 8.4, drop testing of `debian-buster` and `fedora-29`
    
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### 📚 Description

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Prerequisite of:
- #34816
- #35703
- #35801

See also:
- #32074

Instead of fully dropping `debian-buster` (LTS until 2024-06) in the CI,
we replace it by `debian-buster-gcc_spkg` to verify that users on this
platform have the recourse of installing a newer GCC.

We also remove `linuxmint-19.3-gcc_8-python3.8` and change
`fedora-30-python3.8` to `fedora-30` (which builds python from spkg), to
prevent a merge conflict with
#35404

We also add `debian-trixie` (= current testing).

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### ⌛ Dependencies

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URL: #35810
Reported by: Matthias Köppe
Reviewer(s): Dima Pasechnik

Author: Release Manager

.github/workflows/docker.yml

@@ -23,9 +23,10 @@ on:
            "ubuntu-kinetic",
            "ubuntu-lunar",
            "ubuntu-mantic",
-           "debian-buster",
+           "debian-buster-gcc_spkg",
            "debian-bullseye",
            "debian-bookworm",
+           "debian-trixie",
            "debian-sid",
            "linuxmint-20.1",
            "linuxmint-20.2",
@@ -57,7 +58,6 @@ on:
            "opensuse-tumbleweed-python3.10",
            "conda-forge",
            "ubuntu-bionic-gcc_8-i386",
-           "debian-buster-i386",
            "debian-bullseye-i386",
            ]
       tox_packages_factors:

README.md

@@ -189,8 +189,8 @@ in the Installation Guide.
 
 3.  [Linux, WSL] Install the required minimal build prerequisites.
 
-    - Compilers: `gcc`, `gfortran`, `g++` (GCC 8.x to 12.x and recent
-      versions of Clang (LLVM) are supported).
+    - Compilers: `gcc`, `gfortran`, `g++` (GCC versions from 8.4.0 to 13.x
+      and recent versions of Clang (LLVM) are supported).
       See [build/pkgs/gcc/SPKG.rst](build/pkgs/gcc/SPKG.rst) and
       [build/pkgs/gfortran/SPKG.rst](build/pkgs/gfortran/SPKG.rst)
       for a discussion of suitable compilers.

build/pkgs/gcc/SPKG.rst

@@ -6,7 +6,7 @@ Description
 
 This package represents the required C and C++ compilers.
 
-- GCC (GNU Compiler Collection) versions 8.x to 12.x are supported.
+- GCC (GNU Compiler Collection) versions 8.x (>= 8.4.0) to 13.x are supported.
 
 - Clang (LLVM) is also supported.
 
@@ -25,7 +25,7 @@ need to run::
 Vendor and versions of the C and C++ compilers should match.
 
 Users of older Linux distributions (in particular, ``ubuntu-xenial``
-or older, ``debian-stretch`` or older, ``linuxmint-18`` or older)
+or older, ``debian-buster`` or older, ``linuxmint-18`` or older)
 should upgrade their systems before attempting to install Sage from
 source.  Users of ``ubuntu-bionic``, ``linuxmint-19.x``, and
 ``opensuse-15.x`` can install a versioned ``gcc`` system package

build/pkgs/gcc/spkg-configure.m4

@@ -161,8 +161,8 @@ SAGE_SPKG_CONFIGURE_BASE([gcc], [
             # Add the .0 because Debian/Ubuntu gives version numbers like
             # 4.6 instead of 4.6.4 (Trac #18885)
             AS_CASE(["$GXX_VERSION.0"],
-                [[[0-7]].*], [
-                    # Install our own GCC if the system-provided one is older than gcc 8
+                [[[0-7]].*|8.[[0-3]].*], [
+                    # Install our own GCC if the system-provided one is older than gcc 8.4
                     SAGE_SHOULD_INSTALL_GCC([you have $CXX version $GXX_VERSION, which is quite old])
                 ],
                 [1[[4-9]].*], [

tox.ini

@@ -238,6 +238,7 @@ setenv =
     debian-bullseye:  BASE_TAG=bullseye
     debian-bullseye:                           IGNORE_MISSING_SYSTEM_PACKAGES=yes
     debian-bookworm:  BASE_TAG=bookworm
+    debian-trixie:    BASE_TAG=trixie
     debian-sid:       BASE_TAG=sid
     #
     # https://hub.docker.com/u/linuxmintd