s390x: Fix turbofan c linkage

In C to WASM stubs, when number of parameters is more than 5, or
anything requires stack arguments, current linkage is faulty
because of missing STACK_SHADOW_WORDS

Drive-by: Also cleanup s390 code which is not supported anymore.

R=joransiu@ca.ibm.com

Change-Id: I7405c32fd94e158e6868f9ce7d4390c995078dbb
Reviewed-on: https://chromium-review.googlesource.com/c/1257269Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#56352}

src/compiler/c-linkage.cc

@@ -117,6 +117,7 @@ namespace {
 // ===========================================================================
 // == s390x ==================================================================
 // ===========================================================================
+#define STACK_SHADOW_WORDS 20
 #define PARAM_REGISTERS r2, r3, r4, r5, r6
 #define CALLEE_SAVE_REGISTERS \
   r6.bit() | r7.bit() | r8.bit() | r9.bit() | r10.bit() | ip.bit() | r13.bit()
@@ -124,15 +125,6 @@ namespace {
   d8.bit() | d9.bit() | d10.bit() | d11.bit() | d12.bit() | d13.bit() | \
       d14.bit() | d15.bit()
 
-#elif V8_TARGET_ARCH_S390
-// ===========================================================================
-// == s390 ===================================================================
-// ===========================================================================
-#define PARAM_REGISTERS r2, r3, r4, r5, r6
-#define CALLEE_SAVE_REGISTERS \
-  r6.bit() | r7.bit() | r8.bit() | r9.bit() | r10.bit() | ip.bit() | r13.bit()
-#define CALLEE_SAVE_FP_REGISTERS (d4.bit() | d6.bit())
-
 #else
 // ===========================================================================
 // == unknown ================================================================

src/compiler/s390/instruction-selector-s390.cc

@@ -2162,6 +2162,7 @@ void InstructionSelector::EmitPrepareArguments(
     // Poke any stack arguments.
     int slot = kStackFrameExtraParamSlot;
     for (PushParameter input : (*arguments)) {
+      if (input.node == nullptr) continue;
       Emit(kS390_StoreToStackSlot, g.NoOutput(), g.UseRegister(input.node),
            g.TempImmediate(slot));
       ++slot;