"make dist" support

[Joseph S. Myers]

gcc/Makefile.in (and some other files) seems to include some machinery for
"make dist" (see targets distdir, diff etc.).  It looks like these are
obsolete targets creating an old-style gcc-2.8 style distribution; could
someone confirm whether these targets are no longer used in creating
distribution tarballs and diffs and can safely be removed?

-- 
Joseph S. Myers
jsm28@cam.ac.uk