My vim doesn't use iwhiteeol by default:
*'dip'* *'diffopt'*
'diffopt' 'dip' string (default "internal,filler")
global
{not available when compiled without the |+diff|
feature}
Option settings for diff mode. It can consist of the following items.
All are optional. Items must be separated by a comma.
But to disable it:
set diffopt-=iwhiteeol
You can also
set list listchars^=trail:.
to show trailing whitespace