support clean calls with stack padding and memory opnds

From bruen...@google.com on February 19, 2014 15:45:39

We have not hit this before because we pass -mpreferred-stack-boundary=2 on Linux.

On 32-bit MacOS, though, we have stack alignment and we have args passed on the stack. We need to update insert_parameter_preparation() to handle this situation and have it procure some scratch registers in a safe manner.

Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1370