tools: Cleanup EXTRA_WARNINGS

tools: Cleanup EXTRA_WARNINGS

Use += instead of the bash syntax, as Sam Ravnborg suggests. Also, sort
the -W options alphabetically and (... keep them sorted).

Suggested-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: http://lkml.kernel.org/r/1334162178-17152-3-git-send-email-bp@amd64.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>