patch 8.1.0106: build fails when HAVE_DATE_TIME is undefined

Problem:    Build fails when HAVE_DATE_TIME is undefined.
Solution:   Always define init_longVersion(). (Christian Brabandt,
            closes #3075)

src/version.c

@@ -71,6 +71,12 @@ init_longVersion(void)
# endif
#else
char	*longVersion = VIM_VERSION_LONG;

    void
init_longVersion(void)
{
    // nothing to do
}
#endif

static void list_features(void);
@@ -783,6 +789,8 @@ static char *(features[]) =

static int included_patches[] =
{   /* Add new patch number below this line */
/**/
    106,
/**/
    105,
/**/