[doc, committed] fix formatting in @gccoptlist environments

[Sandra Loosemore]

When I was working on some other doc fixes I noticed that there were a 
few cases of lines overflowing the right margin in some of the option 
summary lists.  So when I was fixing that, I noticed some other 
formatting inconsistencies, like only one space instead of two 
separating options on the same line, or a stray @gol at the end of the 
list that resulted in extra vertical whitespace.  I ended up making a 
pass through all the @gccoptlist uses in invoke.texi to scan for such 
things.  There are no changes in content in this patch, just whitespace 
and line break cleanups.

-Sandra
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