CI: move gcc cross build to Ubuntu for newer mingw-w64

The build requires headers that are only available in v12 (processsnapshot.h)
and Arch is still on v12. So move things to Ubuntu.

Similarely to other cross builds remove the system libs configure flags, those
were never there and now fail properly with the 3.12 build system.

.github/workflows/mingw.yml

@@ -161,13 +161,21 @@ jobs:
   cross-gcc-x86_64:
     runs-on: ubuntu-latest
     container:
-      image: archlinux:base-devel
+      image: ubuntu:24.10
     steps:
       - uses: actions/checkout@v3
       - name: Install deps
         run: |
-          pacman --noconfirm -Suuy
-          pacman --needed --noconfirm -S mingw-w64-gcc autoconf-archive autoconf automake zip
+          apt-get update
+          DEBIAN_FRONTEND=noninteractive apt-get install -y \
+            gcc-mingw-w64-x86-64 \
+            g++-mingw-w64-x86-64 \
+            autoconf-archive \
+            autoconf \
+            automake \
+            zip \
+            make \
+            pkg-config
 
       - uses: actions/setup-python@v4
         with:
@@ -188,9 +196,6 @@ jobs:
             --host=x86_64-w64-mingw32 \
             --build=x86_64-pc-linux-gnu \
             --enable-shared \
-            --with-system-expat \
-            --with-system-ffi \
-            --with-system-libmpdec \
             --without-ensurepip \
             --enable-loadable-sqlite-extensions \
             --with-build-python=yes