bug#43225: Grep treats extended Latin characters like whitespace

[Mayo Fark]

What I did:
```
grep -Riw cone *
'''

Expected result: lines with the word "cone" surrounded by whitespace, ignoring 
case.

What I got instead:
```
data/po/pt_BR.po:msgstr "Pressione o ícone de pódio para iniciar o tutorial"
'''

Why this is a bug: the word ícone is not the same as cone and should not have 
been returned in the result set. It appears that grep treats the í character in 
ícone as whitespace, which affects other extended-Latin characters as well.