Experimental support for SDL_mixer

Now working. We need support for SDL 3.4.0 but current wayland
dependency is not fulfilled.

scripts/bootstrap_sdl_mixer_linux.sh

@@ -0,0 +1,73 @@
+#!/usr/bin/env bash
+# One-time bootstrap: builds SDL2_mixer from source and installs it into prebuilt/linux/.
+# SDL3 must already be bootstrapped via bootstrap_sdl_linux.sh before running this.
+# Run this once on the Linux remote after cloning. Re-run only when upgrading SDL2_mixer.
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
+SDL_MIXER_VERSION="${1:-2.8.1}"
+BUILD_TYPE="${2:-Release}"
+BUILD_DIR="$PROJECT_ROOT/out/build/_sdl_mixer_bootstrap/linux"
+PREBUILT_DIR="$PROJECT_ROOT/prebuilt/linux"
+SDL_MIXER_SOURCE="$BUILD_DIR/SDL2_mixer-src"
+
+# Install build dependencies (Debian 12 bookworm)
+echo "Checking build dependencies..."
+sudo apt-get update -qq
+sudo apt-get install -y --no-install-recommends \
+    ninja-build cmake build-essential \
+    gcc-12 g++-12 \
+    libmpg123-dev libopusfile-dev libvorbis-dev libflac-dev
+
+# Download SDL2_mixer source if not already present
+if [ ! -d "$SDL_MIXER_SOURCE" ]; then
+    echo ""
+    echo "=== Downloading SDL2_mixer $SDL_MIXER_VERSION ==="
+    mkdir -p "$BUILD_DIR"
+    curl -L "https://github.com/libsdl-org/SDL_mixer/releases/download/release-${SDL_MIXER_VERSION}/SDL2_mixer-${SDL_MIXER_VERSION}.tar.gz" \
+        | tar -xz -C "$BUILD_DIR"
+    mv "$BUILD_DIR/SDL2_mixer-${SDL_MIXER_VERSION}" "$SDL_MIXER_SOURCE"
+fi
+
+build_sdl_mixer() {
+    local LINK_TYPE="$1"
+    local SHARED="OFF"
+    local STATIC="OFF"
+
+    if [ "$LINK_TYPE" = "dynamic" ]; then SHARED="ON"; else STATIC="ON"; fi
+
+    local OUT_DIR="$PREBUILT_DIR/SDL2_mixer-$LINK_TYPE"
+    local BUILD_OUT="$BUILD_DIR/$LINK_TYPE"
+
+    echo ""
+    echo "=== Building SDL2_mixer ($LINK_TYPE) for Linux ==="
+
+    # Wipe any stale build directory to avoid corrupted cache issues
+    if [ -d "$BUILD_OUT" ]; then
+        echo "Removing stale build directory: $BUILD_OUT"
+        rm -rf "$BUILD_OUT"
+    fi
+
+    cmake -S "$SDL_MIXER_SOURCE" -B "$BUILD_OUT" \
+        -G "Ninja" \
+        -DCMAKE_BUILD_TYPE="$BUILD_TYPE" \
+        -DCMAKE_INSTALL_PREFIX="$OUT_DIR" \
+        -DCMAKE_C_COMPILER=gcc-12 \
+        -DCMAKE_CXX_COMPILER=g++-12 \
+        -DSDL2MIXER_SHARED="$SHARED" \
+        -DSDL2MIXER_STATIC="$STATIC" \
+        -DSDL2MIXER_INSTALL=ON \
+        -DSDL2MIXER_SAMPLES=OFF \
+        -DSDL2MIXER_MIDI_FLUIDSYNTH=OFF \
+        -DSDL2MIXER_WAVPACK=OFF \
+        -DSDL3_DIR="$PREBUILT_DIR/SDL3-$LINK_TYPE/lib/cmake/SDL3"
+
+    cmake --build "$BUILD_OUT"
+    cmake --install "$BUILD_OUT"
+
+    echo "=== Done: $OUT_DIR ==="
+}
+
+build_sdl_mixer "dynamic"
+build_sdl_mixer "static"