In .Bd -literal, break the output line after the last element of each

In .Bd -literal, break the output line after the last element of each
input line, not after the first element.  Since free-form text lines
only have a single element in literal mode, this is only relevant for
macro lines inside literal displays, and only for those containing
more than one macro.  Fixes e.g. awk(1) and boot_config(8).
Note this fix differs from what kristaps@ committed to bsd.lv because
those changes introduce regressions with respect to blank lines in
literal mode.
With permission from deraadt@ to still fix bugs in mandoc.