Add Windows cross-compilation via MinGW, and fix Docker build permission

issues on vboxsf-mounted checkouts

New `make dist-win`/`package-win` targets (folded into `dist`/`package`
alongside the renamed `dist-linux`/`package-linux`) cross-compile
systemshock.exe via MinGW, using prebuilt SDL2/SDL2_mixer/GLEW/
fluidsynth-lite baked into the build-image - no Windows machine or Wine
needed to build it, confirmed working and playable on a real Windows
machine. dist-win/ ships DLLs flat alongside the exe plus a new
res/run.bat launcher, packaged into a .zip the same way dist/ becomes a
.tar.gz.

Also fixes three build-image bugs hit while testing on a VirtualBox
vboxsf-mounted checkout: build-engine.sh/docker-entrypoint.sh losing
their execute bit (chmod +x on restrictive source perms), the container
user missing access to /workspace's supplementary vboxsf group, and
cp -a failing on symlink/hard-link creation (vboxsf doesn't support
either) - now falls back to dereferencing copies when detected. Also
adds Docker/zip/etc. prerequisites to the README for both the desktop
and Quest builds.

build-image/build-engine-win.sh

@@ -0,0 +1,106 @@
+#!/usr/bin/env bash
+# Cross-compiles engine/ (the vendored Shockolate snapshot) for Windows
+# (x86_64) via MinGW, against the dependencies prebuilt into this image at
+# /opt/prebuilt/win - no network access needed. engine/CMakeLists.txt
+# already has working WIN32/MINGW branches (the upstream Shockolate
+# project's own build_win64.sh/appveyor.yml build the same way, natively
+# on Windows via Git Bash/MinGW; this cross-compiles the same branches
+# fully offline and reproducibly from Linux instead), so no source
+# patching is needed, unlike the Quest build's android/engine-patches/.
+#
+# Builds from a scratch copy of engine/ (like android/engine-patches/
+# does for the Quest build) rather than engine/ itself: its BUNDLED
+# dependency paths (build_ext/built_sdl etc.) and in-source CMake cache
+# are relative to/inside the source tree, and would otherwise collide
+# with the Linux desktop build's own build_ext/CMakeCache.txt (see
+# build-engine.sh) if both are built from the same checkout, as `make
+# dist` (dist-linux + dist-win) does.
+#
+# Must be run with the repo root as the working directory - either via
+# ../run-image.sh, or directly when already inside this image (see the
+# Makefile's `engine-win` target, which picks whichever of these
+# applies, same as `engine`).
+#
+# Output lands in engine/.build-output-win/: systemshock.exe, the DLLs
+# it needs at runtime, and a default MIDI soundfont - everything the
+# root Makefile needs to assemble dist-win/.
+set -euo pipefail
+
+REPO_ROOT="$(pwd)"
+SCRATCH_ENGINE="$REPO_ROOT/build/win-engine"
+OUT_DIR="$REPO_ROOT/engine/.build-output-win"
+
+echo "== Preparing a scratch copy of engine/ for the Windows cross-build =="
+rm -rf "$SCRATCH_ENGINE"
+mkdir -p "$(dirname "$SCRATCH_ENGINE")"
+
+# See build-engine.sh for why this detection is needed (e.g. a VirtualBox
+# vboxsf shared folder refusing to create symlinks or preserve hard-link
+# relationships) - applied here too since build/ is under the same
+# bind-mounted repo checkout.
+CP_FLAGS=(-a)
+mkdir -p "$(dirname "$SCRATCH_ENGINE")/.symlink-test-dir"
+if ! ln -s test-target "$(dirname "$SCRATCH_ENGINE")/.symlink-test-dir/test" 2>/dev/null; then
+    echo "(destination filesystem doesn't support symlinks - copying real file content instead)"
+    CP_FLAGS=(-a --dereference --no-preserve=links)
+fi
+rm -rf "$(dirname "$SCRATCH_ENGINE")/.symlink-test-dir"
+
+cp "${CP_FLAGS[@]}" "$REPO_ROOT/engine" "$SCRATCH_ENGINE"
+cd "$SCRATCH_ENGINE"
+
+# If engine/ has ever been built in-source directly (`make dist`/`make
+# engine` - see build-engine.sh), that leftover CMakeCache.txt etc. just
+# got copied along verbatim - and it still points at the real engine/
+# path, not this scratch copy, which CMake refuses to configure against
+# ("directory is different than the directory where CMakeCache.txt was
+# created"). Same artifact list as .gitignore's "Engine build artifacts"
+# section.
+rm -rf build_ext CMakeCache.txt CMakeFiles cmake_install.cmake Makefile \
+    systemshock src/Libraries/CMakeFiles
+
+echo "== Wiring up prebuilt SDL2/SDL2_mixer/GLEW/fluidsynth-lite (Windows/MinGW) from the image =="
+rm -rf build_ext
+mkdir -p build_ext
+cp "${CP_FLAGS[@]}" /opt/prebuilt/win/sdl2 build_ext/built_sdl
+cp "${CP_FLAGS[@]}" /opt/prebuilt/win/sdl2_mixer build_ext/built_sdl_mixer
+cp "${CP_FLAGS[@]}" /opt/prebuilt/win/glew build_ext/built_glew
+# engine/CMakeLists.txt's BUNDLED FluidSynth mode hardcodes
+# build_ext/fluidsynth-lite/src as the library search path (matching the
+# desktop Linux in-source build's own output layout) - same lib/ -> src/
+# remapping build-image/prepare-android-project.sh does for the Quest
+# build's own prebuilt fluidsynth-lite.
+mkdir -p build_ext/fluidsynth-lite/src build_ext/fluidsynth-lite/include
+cp "${CP_FLAGS[@]}" /opt/prebuilt/win/fluidsynth-lite/lib/. build_ext/fluidsynth-lite/src/
+cp "${CP_FLAGS[@]}" /opt/prebuilt/win/fluidsynth-lite/include/. build_ext/fluidsynth-lite/include/
+
+echo "== Configuring (CMake, MinGW cross-compile, BUNDLED SDL2/SDL2_mixer/FluidSynth) =="
+cmake -DCMAKE_TOOLCHAIN_FILE="$MINGW_TOOLCHAIN_FILE" \
+    -DENABLE_SDL2=BUNDLED -DENABLE_SOUND=BUNDLED -DENABLE_FLUIDSYNTH=BUNDLED .
+
+echo "== Compiling =="
+make -j"$(nproc)" systemshock
+
+echo "== Assembling engine/.build-output-win =="
+rm -rf "$OUT_DIR"
+mkdir -p "$OUT_DIR"
+cp systemshock.exe "$OUT_DIR/"
+# Only SDL2.dll/SDL2_mixer.dll themselves - not SDL2_mixer's own bundled
+# codec DLLs (libvorbis, libmodplug, libopus, ...), matching what
+# engine/'s own upstream Windows build script (build_win64.sh) ships:
+# Shockolate only ever calls Mix_LoadWAV_RW/Mix_HookMusic (same as the
+# Quest build - see build-image/Dockerfile's Android layer comment),
+# never loading the OGG/MOD/MP3 game data those codecs would be for.
+cp build_ext/built_sdl/bin/SDL2.dll build_ext/built_sdl_mixer/bin/SDL2_mixer.dll "$OUT_DIR/"
+cp build_ext/built_glew/lib/glew32.dll "$OUT_DIR/"
+cp build_ext/fluidsynth-lite/src/*.dll "$OUT_DIR/"
+# libgcc/libstdc++ are statically linked (see the Dockerfile's
+# MINGW_TOOLCHAIN_FILE), but fluidsynth-lite/SDL2 still pull in the
+# MinGW pthread emulation dynamically.
+cp /usr/x86_64-w64-mingw32/lib/libwinpthread-1.dll "$OUT_DIR/"
+cp /opt/prebuilt/soundfont/default.sf2 "$OUT_DIR/soundfont.sf2"
+
+echo "== Done =="
+echo "Binary:     $OUT_DIR/systemshock.exe"
+echo "DLLs:       $OUT_DIR/*.dll"
+echo "Soundfont:  $OUT_DIR/soundfont.sf2"