Subzero. ARM32. No more SP frobbing.

Pre-computes the max stack size outgoing arguments, and pre-allocates
it during prolog, deallocating during epilog.

With this CL, there are no more StackAdjustments needed for the ARM32,
which will simplify rematerializing alloca'd variables.

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

Review URL: https://codereview.chromium.org/1467473003 .
diff --git a/src/IceTargetLowering.h b/src/IceTargetLowering.h
index 5489b8b..1350afa 100644
--- a/src/IceTargetLowering.h
+++ b/src/IceTargetLowering.h
@@ -311,6 +311,7 @@
   virtual void lowerOther(const Inst *Instr);
 
   virtual void genTargetHelperCallFor(Inst *Instr) = 0;
+  virtual uint32_t getCallStackArgumentsSizeBytes(const InstCall *Instr) = 0;
 
   virtual void doAddressOptLoad() {}
   virtual void doAddressOptStore() {}