构建 squashfs 工具时出现编译错误

Question

我尝试编译取消压缩来自 GPL 源的工具，源位于“squashfs-tools”目录中。执行时make出现错误：Makefile:2: *** Sqlzma is not defined. Stop.据我所知，sqlzma 文件（sqlzma.h？）位于另一个目录“sqlzma-3.4-457”中。

squashfs-tools 目录内容：

生成文件：

ifndef Sqlzma
$(error Sqlzma is not defined)
endif

INSTALL_DIR = /usr/local/bin

INCLUDEDIR = .

CFLAGS := -I$(INCLUDEDIR) -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_GNU_SOURCE -O2
ifdef UseDebugFlags
DebugFlags = -g -Wall -Wno-unused-variable -O0 -UNDEBUG
endif
CFLAGS += -I${Sqlzma} -D_REENTRANT -DNDEBUG ${DebugFlags}
LDFLAGS += -L${LzmaAlone} -L${LzmaC}

all: mksquashfs unsquashfs

mksquashfs: mksquashfs.o read_fs.o sort.o
    #$(CC) $(LDFLAGS) mksquashfs.o read_fs.o sort.o -lz -lpthread -lm -lunlzma_r -llzma_r -lstdc++ -o $@
    g++ $(LDFLAGS) mksquashfs.o read_fs.o sort.o -lz -lpthread -lm -lunlzma_r -llzma_r -lstdc++ -o $@

mksquashfs.o: mksquashfs.c squashfs_fs.h mksquashfs.h global.h sort.h \
    ${Sqlzma}/sqlzma.h ${Sqlzma}/sqmagic.h \
    ${LzmaAlone}/liblzma_r.a ${LzmaC}/libunlzma_r.a

read_fs.o: read_fs.c squashfs_fs.h read_fs.h global.h \
    ${Sqlzma}/sqlzma.h ${Sqlzma}/sqmagic.h

sort.o: sort.c squashfs_fs.h global.h sort.h

unsquashfs: unsquashfs.o
    $(CC) $(LDFLAGS) unsquashfs.o -lpthread -lm -lunlzma -lz -o $@

unsquashfs.o: unsquashfs.c squashfs_fs.h read_fs.h global.h \
    ${Sqlzma}/sqlzma.h ${Sqlzma}/sqmagic.h ${LzmaC}/libunlzma.a

clean:
    -rm -f *.o mksquashfs unsquashfs

install: mksquashfs unsquashfs
    mkdir -p $(INSTALL_DIR)
    cp mksquashfs unsquashfs $(INSTALL_DIR)

“安装”自述文件中还有一小段说明：

2. Building squashfs tools
--------------------------
The squashfs-tools directory contains the mksquashfs and unsquashfs programs.
These can be made by typing make.  The source files use a local copy of
squashfs_fs.h (included in the kernel patches) allowing the tools to be made
without needing to patch the kernel.

请指教如何编译 unsquashfs 和 mksquashfs 二进制文件（不影响我的 Ubuntu 16.04 安装）。

编辑：链接到来源。