Fix unit test French locate checks for glibc >= 2.8.

Fix unit test French locate checks for glibc >= 2.8.

Until 2.7 glibc wrongly used periods instead of slashes as separators for the
French date format and the test accounted for this, breaking it with recent
glibc versions in which this bug was fixed.

Fix this by limiting the workaround to the old glibc versions only.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70629 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775