[wwwdocs] gcc-14/changes.html: OpenMP - improve wording

[Tobias Burnus]

The attached patch does a tiny updated to the OpenMP features (AMD GCN 
now also has an optimized memcpy_rect not only nvptx), but the main 
change is some shifting around to make it more consistent and better 
readable.

I intend to commit this relatively soon; like always, comments and 
suggestions are welcome - be it before or after the commit.

Current version: http://gcc.gnu.org/gcc-14/changes.html

Thanks,

Tobias