Build: Add very limited experimental CMake support.

This version matches CMake files in the master branch (commit
265daa873c0d871f5f23f9b56e133a6f20045a0a) except that this omits
two source files that aren't in v5.2 and in the beginning of
CMakeLists.txt the first paragraph in the comment is slightly
different to point out possible issues in building shared liblzma.