CogVM source as per VMMaker.oscog-eem.1332/r3365
Newspeak Cogit:
Fix the regression in implicit receiver sends caused by VMMaker.oscog-eem.1317
(fix to performance regression caused by using XCHG on x86).
The implicit receiver cache uses SendNumArgsReg to refer to the cache object.
Hence we must use TempReg for genPushRegisterArgsForNumArgs: in this case.
So refactor to genPushRegisterArgsForNumArgs:scratchReg:, passing either
TempReg or SendNumArgsReg as approprate.
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