Fix RandomX validation exploit with difficulty reset, improve build system

- One-time difficulty reset to minimum for 17 blocks at activation height
- Separate RandomX build dirs for linux/win64 cross-compilation
- Add build target tracking to auto-clean on target switch
- Automated win64 release packaging to release-win64/
- Add build artifacts to .gitignore
- Miner memory diagnostics and large-page dataset fallback

build.sh

@@ -5,13 +5,52 @@
 
 set -eu -o pipefail
 
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+BUILD_TARGET_FILE="$SCRIPT_DIR/src/.build_target"
+
+# Function to check and clean if target changed
+check_and_clean_target() {
+    local new_target="$1"
+    local current_target=""
+    
+    if [[ -f "$BUILD_TARGET_FILE" ]]; then
+        current_target=$(cat "$BUILD_TARGET_FILE")
+    fi
+    
+    if [[ -n "$current_target" && "$current_target" != "$new_target" ]]; then
+        echo "Build target changed from '$current_target' to '$new_target'"
+        echo "Cleaning old build artifacts to prevent cross-compilation contamination..."
+        cd "$SCRIPT_DIR"
+        make distclean 2>/dev/null || true
+        # Clean leveldb separately as it often causes issues
+        if [[ -d src/leveldb ]]; then
+            make -C src/leveldb clean 2>/dev/null || true
+        fi
+        echo "Clean complete."
+    fi
+    
+    # Record the new target
+    echo "$new_target" > "$BUILD_TARGET_FILE"
+}
+
+# Check for --win-release flag for cross-compilation
+if [[ "${1:-}" == "--win-release" ]]; then
+    check_and_clean_target "windows"
+    shift
+    ./util/build-win.sh "$@"
+    exit $?
+fi
+
 # run correct build script for detected OS
 if [[ "$OSTYPE" == "linux-gnu"* ]]; then
-    ./util/build.sh --disable-tests $@
+    check_and_clean_target "linux"
+    ./util/build.sh --disable-tests "$@"
 elif [[ "$OSTYPE" == "darwin"* ]]; then
-    ./util/build-mac.sh --disable-tests $@
+    check_and_clean_target "macos"
+    ./util/build-mac.sh --disable-tests "$@"
 elif [[ "$OSTYPE" == "msys"* ]]; then
-    ./util/build-win.sh --disable-tests $@
+    check_and_clean_target "windows"
+    ./util/build-win.sh --disable-tests "$@"
 #elif [[ "$OSTYPE" == "freebsd"* ]]; then
     # placeholder
 else