Wording for errno in manual pages

[Roland Illig <roland.illig%gmx.de@localhost>]

In the manual pages, there are several different wordings around errno:

An error code is stored in the external variable "errno".
An error code is stored in the global variable "errno".
An error code is stored in the global "errno".
An error code is stored in "errno".

I'd like to unify all these different wordings, and I prefer the latter
wording, leaving open whether errno is a global variable or a
thread-local variable.

Any known caveats, other than skipping any files in .../dist/...?