Split out some of the addProlog code from x86 and
reuse that for ARM. Mainly, the code that doesn't
concern preserved registers or stack arguments is split out.

ARM push and pop take a whole list of registers (not
necessarily consecutive, but should be in ascending order).
There is also "vpush" for callee-saved float/vector
registers but we do not handle that yet (the register
numbers for that have to be consecutive).

Enable some of the int-arg.ll tests, which relied on
addPrologue's finishArgumentLowering to pull from the
correct argument stack slot.

Test some of the frame pointer usage (push/pop) when
handling a variable sized alloca.

Also change the classification of LR, and PC so that
they are not "CalleeSave". We don't want to push LR
if it isn't overwritten by another call. It will certainly be
"used" by the return however. The prologue code only checks
if a CalleeSave register is used somewhere before deciding
to preserve it. We could make that stricter and check if
the register is also written to, but there are some
additional writes that are not visible till after the
push/pop are generated (e.g., copy from argument stack slot
to the argument register). Instead, keep checking use
only, and handle LR as a special case (IsLeafFunction).

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4076
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1159013002