redundant % signs in output_operand_lossage

[Stan Shebs]

While bootstrapping with my Darwin patches, I got an internal error
that said "output_operand: invalid %%K value", which seemed odd,
since "%%K" is not a part of machine descriptions.  From rooting
around a bit and finding many messages like this, and some not,
I gather that the message used to be a format string, but is now
output literally, and the %% can just be %.  Anyway, since I can't
test any of the potentially affected architectures except rs6000,
I'll have to leave this as a suggestion for maintainers.  I noticed
this in a29k, alpha, ia64, romp, rs6000, and sparc.

Stan