I don't see this in the sources
(https://svn.filezilla-project.org/filezilla/libfilezilla/tags/0.9.0/).
I'm
pretty sure those GPLv3 licensed files are part of the GNU
autotools rather than libfilezilla.
libfilezilla-0.9.0/config/test-driver:# the Free Software Foundation;
either version 2, or (at your option)
libfilezilla-0.9.0/configure:# published by the Free Software
Foundation; either version 2 of
libfilezilla-0.9.0/COPYING: the Free Software Foundation; either
version 2 of the License, or
libfilezilla-0.9.0/m4/ax_check_link_flag.m4:# Free Software
Foundation, either version 3 of the License, or (at your
libfilezilla-0.9.0/m4/ax_check_compile_flag.m4:# Free Software
Foundation, either version 3 of the License, or (at your
libfilezilla-0.9.0/m4/libtool.m4:# published by the Free Software
Foundation; either version 2 of
libfilezilla-0.9.0/m4/ax_append_flag.m4:# Free Software Foundation,
either version 3 of the License, or (at your
m4 is part of autotools, which is GPLv3. It's not part of the
libfilezilla project.
libfilezilla-0.9.0/README:the Free Software Foundation; either version
2 of the License, or