ARM estimateStackSize() needs to account for simplified call frames.

If the function allocates reserved stack space for callee argument frames,
estimateStackSize() needs to account for that, as it doesn't show up as
ordinary frame objects. Otherwise, a callee with a large argument list will
throw off the calculations for whether to allocate an emergency spill slot
and we get assert() failures in the register scavenger.

rdar://9715469

llvm-svn: 134415