Whenever I fit brake pads if they are not supplied with a chamfer on the leading edge I just use a wide hand file and cut an angle on the leading edge.
If you look at the wheel rotation the leading edge is the first contact side - the other side of the pad is the trailing edge. I usually just take off the corner so as to speak.
Modern pads typically look like this - with motorcycle pads being much smaller in area you only need to angle the leading edge by 2 or 3 mm at around 30 deg if the squeal returns after a few thousand miles repeat.
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modern pad by
Macabe Thiele, on Flickr