secilc: do not build secilc man page if it is up to date

When running "make all" several times in the root directory of the
project, the following lines always appear (and the command takes some
seconds to complete on my system with a slow hard drive):

    xmlto man secilc.8.xml
    Note: Writing secilc.8

This is because "make man" always builds secilc.8 even though
secilc.8.xml has not been modified. Introduce an intermediate target to
avoid this behavior.

Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>
1 file changed