Transparently use lzma, if available in system

It will get picked up by libtiff, so make sure we provide it when
linking libimage

.travis.yml

@@ -5,7 +5,7 @@ before_install:
     - sudo add-apt-repository --yes ppa:beineri/opt-qt551-trusty
     - sudo apt-get update
 install:
-    - sudo apt-get install -y liblzo2-dev liblz4-dev libfreetype6-dev libpng-dev libsdl2-dev libglew-dev freeglut3-dev qt55script libsuperlu3-dev libpng-dev qt55svg qt55tools wget libusb-1.0-0-dev libboost-all-dev
+    - sudo apt-get install -y liblzo2-dev liblz4-dev libfreetype6-dev libpng-dev libsdl2-dev libglew-dev freeglut3-dev qt55script libsuperlu3-dev libpng-dev qt55svg qt55tools wget libusb-1.0-0-dev libboost-all-dev liblzma-dev
     # someone forgot to include liblz4.pc with the package, use the version from xenial, as it only depends on libc
     - wget http://mirrors.kernel.org/ubuntu/pool/main/l/lz4/liblz4-1_0.0~r131-2ubuntu2_amd64.deb -O liblz4.deb
     - wget http://mirrors.kernel.org/ubuntu/pool/main/l/lz4/liblz4-dev_0.0~r131-2ubuntu2_amd64.deb -O liblz4-dev.deb

toonz/sources/CMakeLists.txt

@@ -230,7 +230,6 @@ elseif(UNIX)
     find_library(Z_LIB z)
 
     find_package(TIFF REQUIRED)
-    set(TIFF_LIB ${TIFF_LIBRARY})
     find_package(PNG REQUIRED)
     set(PNG_LIB ${PNG_LIBRARY})
     message("******* libpng:" ${PNG_LIB})
@@ -244,6 +243,12 @@ elseif(UNIX)
 
     # the libraries have .pc
     find_package(PkgConfig)
+
+    # This is not required for OpenToonz itself, but libtiff will pick it up if
+    # present and libimage won't be aware causing linker to fail
+    pkg_check_modules(LZMA liblzma)
+    set(TIFF_LIB ${TIFF_LIBRARY} ${LZMA_LIBRARIES})
+
     if(GLEW-NOTFOUND)
         pkg_check_modules(GLEW REQUIRED glew)
     endif()