"make dist" now works through git. But lots of makefile still set a "distribute" variable, which as far as I can tell isn't used anywhere. manual/Makefile has additional special support for building a documentation-only distribution, which I think is also bitrotten and obsolete (I guess it's really a relic of smaller disk sizes, when people may have wanted smaller distributions for particular little pieces of packages).
These settings and extra rules in manual/Makefile should be removed.
Remaining after commit a4300c7a4d65e24a4a0215460c063ea9c7b4605a: one setting in sysdeps/s390/s390-64/Makefile, plus the special support in manual/Makefile for doc-only distributions.
commit 7c0616faf51743a7218cf64a2e81bfc977c73a05 removes the s390-64 remains.
A patch for the manual has been sent to the libc-alpha list.
Manual building support is now removed as well, therefore this bug is fixed.