Rich Felker [off-list ref] writes:
This is especially unfriendly when the semantics of the switch come
across, at least to some users, as "your system regex is incomplete"
rather than "git can't use it because git depends on nonstandard
extensions".
The latter is exactly what Makefile patch that brought this change
says, I think.
# Define NO_REGEX if your C library lacks regex support with REG_STARTEND
# feature.
Before the series updated the message to the above, we used to say:
# Define NO_REGEX if you have no or inferior regex support in your C library.
which _was_ unfair to those who needed to set NO_REGEX for whatever
reason. It was totally unclear "inferior" relative to what standard
the message was passing its harsh judgement on your C library.