CMake builtin copy of lzma does not have lzma_stream_encoder_mt
The Utilities/Scripts/update-liblzma.bash
import script brings in the liblzma/common/stream_encoder_mt.c
source file but it is not built by our CMakeLists.txt
file for liblzma. Compiling the source does not work because the import script is missing common/mythread.h
.