Containerised build environment

Create a Dockerfile to enable a portable build environment. The Dockerfile is based on Ubuntu 24.04, and uses multiple stages to produce a minimal final product, with the final image size sitting at about 75mb.
This branch also incorporates the updates prepared by @cole-h to update to squashfs-tools 4.4 in devttys0#56.
Finally, building on newer GCC highlights a dangling pointer error in LzmaEnc.c. I have separated the fix for this problem into a dedicated patch file for ease of review.

Dockerfile

@@ -0,0 +1,40 @@
+FROM ubuntu:24.04 AS builder
+
+RUN --mount=type=cache,target=/var/cache/apt,id=builder-apt-cache \
+    --mount=type=cache,target=/var/lib/apt,id=builder-apt-lib \
+    apt-get update && \
+    apt-get install -y --no-install-recommends \
+        build-essential \
+        git \
+        liblzma-dev \
+        liblzo2-dev \
+        patch \
+        zlib1g-dev \
+    && mkdir -p /sasquatch
+
+WORKDIR /sasquatch
+
+ADD https://downloads.sourceforge.net/project/squashfs/squashfs/squashfs4.4/squashfs4.4.tar.gz .
+RUN tar -zxvf squashfs4.4.tar.gz
+
+COPY patches /sasquatch/patches
+RUN patch -d squashfs4.4 -p1 < patches/0_sasquatch_4.4.patch && \
+    patch -d squashfs4.4 -p1 < patches/1_fix_dangling_pointer.patch && \
+   cd squashfs4.4/squashfs-tools && \
+   make
+
+FROM ubuntu:24.04
+
+RUN --mount=type=cache,target=/var/cache/apt,id=runtime-apt-cache \
+    --mount=type=cache,target=/var/lib/apt,id=runtime-apt-lib \
+    apt-get update && \
+    apt-get install -y --no-install-recommends \
+       liblzma5 \
+       liblzo2-2 \
+       zlib1g
+
+COPY --from=builder /sasquatch/squashfs4.4/squashfs-tools/sasquatch /usr/local/bin/sasquatch
+
+WORKDIR /work
+
+ENTRYPOINT [ "/usr/local/bin/sasquatch" ]

build.sh

@@ -1,5 +1,5 @@
 #!/bin/bash
-# Script to download squashfs-tools v4.3, apply the patches, perform a clean build, and install.
+# Script to download squashfs-tools v4.4, apply the patches, perform a clean build, and install.
 
 # If not root, perform 'make install' with sudo
 if [ $UID -eq 0 ]
@@ -18,20 +18,20 @@ fi
 # Make sure we're working in the same directory as the build.sh script
 cd $(dirname `readlink  -f $0`)
 
-# Download squashfs4.3.tar.gz if it does not already exist
-if [ ! -e squashfs4.3.tar.gz ]
+# Download squashfs4.4.tar.gz if it does not already exist
+if [ ! -e squashfs4.4.tar.gz ]
 then
-    wget https://downloads.sourceforge.net/project/squashfs/squashfs/squashfs4.3/squashfs4.3.tar.gz
+    wget https://downloads.sourceforge.net/project/squashfs/squashfs/squashfs4.4/squashfs4.4.tar.gz
 fi
 
-# Remove any previous squashfs4.3 directory to ensure a clean patch/build
-rm -rf squashfs4.3
+# Remove any previous squashfs4.4 directory to ensure a clean patch/build
+rm -rf squashfs4.4
 
-# Extract squashfs4.3.tar.gz
-tar -zxvf squashfs4.3.tar.gz
+# Extract squashfs4.4.tar.gz
+tar -zxvf squashfs4.4.tar.gz
 
 # Patch, build, and install the source
-cd squashfs4.3
-patch -p0 < ../patches/patch0.txt
+cd squashfs4.4
+patch -p1 < ../patches/*.patch
 cd squashfs-tools
 make && $SUDO make install