This is a partial revert of f1f029c7.

"=rm" is allowed in this context, because "pop" is explicitly defined
to adjust the stack pointer *before* it evaluates its effective
address, if it has one.  Thus, we do end up writing to the correct
address even if we use an on-stack memory argument.

The original reporter for f1f029c7 was
apparently using a broken x86 simulator.

[ Impact: performance ]
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>
Cc: Gabe Black <spamforgabe@umich.edu>