terminology: zero character vs. null character

[Roland Illig]

Hi,

I am currently translating GCC into German. During that, I noticed that
in some places the term "zero character" means '\0'. The official term
though is "null character", as per the C standard.

Since it is confusing to have two different terms for the same concept,
the term "zero character" should be dropped entirely, both because it is
uncommon and because it can be confused with '0'.

Since this affects several places in the code, I think it's better to
start a small discussion first instead of writing several PRs.

Regards,
Roland