emitIAS for push -- simplify push since it's not used for args passing anymore

Since push isn't used for args passing anymore, the cases of handling
push for vectors and floats/doubles isn't needed anymore. Passing
vectors requires a bit more care of alignment, so that was changed.

I can imagine push needing to handle addresses later (at least on
x86-64 to push the lower 32-bits of return address), but for now,
this means only handling GPRs. The XMM registers are not callee saved.

BUG=none
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/633553003
diff --git a/src/IceTargetLoweringX8632.h b/src/IceTargetLoweringX8632.h
index da79c85..271d4a2 100644
--- a/src/IceTargetLoweringX8632.h
+++ b/src/IceTargetLoweringX8632.h
@@ -383,8 +383,8 @@
   void _psub(Variable *Dest, Operand *Src0) {
     Context.insert(InstX8632Psub::create(Func, Dest, Src0));
   }
-  void _push(Operand *Src0, bool SuppressStackAdjustment = false) {
-    Context.insert(InstX8632Push::create(Func, Src0, SuppressStackAdjustment));
+  void _push(Variable *Src0) {
+    Context.insert(InstX8632Push::create(Func, Src0));
   }
   void _pxor(Variable *Dest, Operand *Src0) {
     Context.insert(InstX8632Pxor::create(Func, Dest, Src0));