functions: fix date calculations

In case date(1) does not support nanosecond resolution, it does
not interpret '%N', and leave it as-is. So we have to remove it.

Note that some versions replaces '%N' with 'N', so we have to
take this into account as well.

Reported-by: Kyle Grieb <grieb.kyle@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 reporter_name="YEM"

 reporter_url="http://ymorin.is-a-geek.org/"

 reporter_comment="Sample i586 configuration tweaked to generate code for the geode."