Rollup merge of #125590 - ChrisDenton:mingw-ci-3, r=Kobzol

Add a "Setup Python" action for github-hosted runners and remove unnecessary `CUSTOM_MINGW` environment variable

The Setup Python action isn't strictly necessary ([even on Windows](#125584)) but it is [recommend by GitHub](https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-python#specifying-a-python-version).

The `CUSTOM_MINGW` environment variable is redundant now as it's always set for mingw and always unset otherwise.

try-job: x86_64-mingw
try-job: x86_64-mingw
try-job: dist-x86_64-msvc
try-job: dist-x86_64-mingw

Author: matthiaskrgr

Diff for: .github/workflows/ci.yml

@@ -154,9 +154,12 @@ jobs:
 
       - name: checkout submodules
         run: src/ci/scripts/checkout-submodules.sh
-
-      - name: install MSYS2
-        run: src/ci/scripts/install-msys2.sh
+      
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.x'
+        if: runner.environment == 'github-hosted'
 
       - name: install MinGW
         run: src/ci/scripts/install-mingw.sh

Diff for: src/ci/github-actions/jobs.yml

@@ -378,7 +378,6 @@ auto:
       # We are intentionally allowing an old toolchain on this builder (and that's
       # incompatible with LLVM downloads today).
       NO_DOWNLOAD_CI_LLVM: 1
-      CUSTOM_MINGW: 1
     <<: *job-windows-8c
 
   - image: x86_64-mingw
@@ -390,7 +389,6 @@ auto:
       # We are intentionally allowing an old toolchain on this builder (and that's
       # incompatible with LLVM downloads today).
       NO_DOWNLOAD_CI_LLVM: 1
-      CUSTOM_MINGW: 1
     <<: *job-windows-8c
 
   - image: dist-x86_64-msvc
@@ -439,7 +437,6 @@ auto:
       # incompatible with LLVM downloads today).
       NO_DOWNLOAD_CI_LLVM: 1
       SCRIPT: python x.py dist bootstrap --include-default-paths
-      CUSTOM_MINGW: 1
       DIST_REQUIRE_ALL_TOOLS: 1
     <<: *job-windows-8c
 
@@ -453,7 +450,6 @@ auto:
       # We are intentionally allowing an old toolchain on this builder (and that's
       # incompatible with LLVM downloads today).
       NO_DOWNLOAD_CI_LLVM: 1
-      CUSTOM_MINGW: 1
       DIST_REQUIRE_ALL_TOOLS: 1
     <<: *job-windows-8c
 

Diff for: src/ci/scripts/install-mingw.sh

@@ -1,8 +1,5 @@
 #!/bin/bash
-# If we need to download a custom MinGW, do so here and set the path
-# appropriately.
-#
-# Otherwise install MinGW through `pacman`
+# For mingw builds use a vendored mingw.
 
 set -euo pipefail
 IFS=$'\n\t'
@@ -16,19 +13,16 @@ if isWindows && isKnownToBeMingwBuild; then
     case "${CI_JOB_NAME}" in
         *i686*)
             bits=32
-            arch=i686
             mingw_archive="${MINGW_ARCHIVE_32}"
             ;;
         *x86_64*)
             bits=64
-            arch=x86_64
             mingw_archive="${MINGW_ARCHIVE_64}"
             ;;
         *aarch64*)
             # aarch64 is a cross-compiled target. Use the x86_64
             # mingw, since that's the host architecture.
             bits=64
-            arch=x86_64
             mingw_archive="${MINGW_ARCHIVE_64}"
             ;;
         *)
@@ -38,13 +32,9 @@ if isWindows && isKnownToBeMingwBuild; then
             ;;
     esac
 
-    if [[ "${CUSTOM_MINGW:-0}" == 0 ]]; then
-        pacman -S --noconfirm --needed mingw-w64-$arch-toolchain
-    else
-        mingw_dir="mingw${bits}"
+    mingw_dir="mingw${bits}"
 
-        curl -o mingw.7z "${MIRRORS_BASE}/${mingw_archive}"
-        7z x -y mingw.7z > /dev/null
-        ciCommandAddPath "$(pwd)/${mingw_dir}/bin"
-    fi
+    curl -o mingw.7z "${MIRRORS_BASE}/${mingw_archive}"
+    7z x -y mingw.7z > /dev/null
+    ciCommandAddPath "$(pwd)/${mingw_dir}/bin"
 fi