chore: revert "chore: compile against glibc 2.26"

This reverts commit ae0e0ed1db.

.github/workflows/ci.yml

@@ -49,11 +49,11 @@ jobs:
     strategy:
       matrix:
         include:
-          # portable release build: use channel with older glibc (2.26 as used by e.g. Amazon Linux 2)
+          # portable release build: use channel with older glibc (2.27)
           - name: Linux release
             os: ubuntu-latest
             release: true
-            shell: nix-shell --arg pkgsDist "import (fetchTarball \"https://github.com/NixOS/nixpkgs/archive/0b307aa73804bbd7a7172899e59ae0b8c347a62d.tar.gz\") {{}}" --run "bash -euxo pipefail {0}"
+            shell: nix-shell --arg pkgsDist "import (fetchTarball \"channel:nixos-19.03\") {{}}" --run "bash -euxo pipefail {0}"
             llvm-url: https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-linux-gnu.tar.zst
             prepare-llvm: ../script/prepare-llvm-linux.sh lean-llvm*
             binary-check: ldd -v
@@ -108,7 +108,7 @@ jobs:
             CMAKE_OPTIONS: -DCMAKE_PREFIX_PATH=$GMP -DLEAN_INSTALL_SUFFIX=-linux_aarch64
             release: true
             cross: true
-            shell: nix-shell --arg pkgsDist "import (fetchTarball \"https://github.com/NixOS/nixpkgs/archive/0b307aa73804bbd7a7172899e59ae0b8c347a62d.tar.gz\") {{ localSystem.config = \"aarch64-unknown-linux-gnu\"; }}" --run "bash -euxo pipefail {0}"
+            shell: nix-shell --arg pkgsDist "import (fetchTarball \"channel:nixos-19.03\") {{ localSystem.config = \"aarch64-unknown-linux-gnu\"; }}" --run "bash -euxo pipefail {0}"
             llvm-url: https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-linux-gnu.tar.zst https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-aarch64-linux-gnu.tar.zst
             prepare-llvm: EXTRA_FLAGS=--target=aarch64-unknown-linux-gnu ../script/prepare-llvm-linux.sh lean-llvm-aarch64-* lean-llvm-x86_64-*
       # complete all jobs

doc/setup.md

@@ -4,7 +4,7 @@
 
 Platforms built & tested by our CI, available as nightly releases via elan (see below)
 
-* x86-64 Linux with glibc 2.26+
+* x86-64 Linux with glibc 2.27+
 * x86-64 macOS 10.15+
 * x86-64 Windows 10+