tests: Generate gen-options.awk expected output better.

In the main test group for gen-options.awk, various combinations of
sed and shell line noise are used to create the expected output.

It turns out that at least some versions of Solaris /bin/sed don't
accept patterns like [^\n] as meaning "any character other than
newline", which causes this line noise to fail.  We could perhaps
use /usr/xpg4/bin/sed instead which seems to not have this specific
problem, but let's just do everything in awk which is much simpler.