kbuild: ver_linux fix glibc version print

Fix ver_linux glibc version printing (for real this time)

Alexey Dobriyan reported that commit
4a645d5e
broke ver_linux when glibc has a 3 digit
version number, and proposed a patch.
Al Viro then suggested a simpler way to
solve the problem which I've then simply
put into patch form.

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Signed-off-by: Al Viro <viro@ftp.linux.org.uk>
Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>