lzma.jam doesn't support building from source, like zlib.jam and bzip2.jam

[pdimov]

Would it make sense for lzma.jam to also support building from source?

[grisumbras]

If my PR #296 is merged, then (I think) one could do

lib mylzma : lzma.cpp ;
external.configure lzma : <target>lzma=mylzma ;