Currently the file list generated by Doxygen has src/ at the
beginning of each path. Paths like common/sysdefs.h and
liblzma/api/lzma.h are easier to read without such a prefix.
Builds from a separate build directory with
mkdir build
cd build
../configure
doxygen Doxyfile
include an even longer prefix /home/someone/src/xz/src; this
patch has the nice side-effect of eliminating that prefix, too.