BR 3392534: error out on an inconsistently redefined label
BR 3392534: error out on an inconsistently redefined label

If a label is redefined in the same pass, and the value is
inconsistent, then error out. While we are at it, give the source
location of the previous definition.

This explicitly rejects BR 3392535; there seems to be no reason to
reject duplicate definitions with the same value, as there is no
inconsistency involved.

Signed-off-by: H. Peter Anvin <8a453bad9912ffe59bc0f0b8abe03df9be19379e@zytor.com>

techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm