liblzma: Add missing #ifdefs to filter_common.c.
liblzma: Add missing #ifdefs to filter_common.c.

Passing --disable-decoders to configure broke a few
encoders due to missing #ifdefs in filter_common.c.

Thanks to Jason Gorski for the patch.

pombreda/go-liblzma,pombreda/go-liblzma,pombreda/go-liblzma