[wasm] Initialize the root register for WASM tests.

src/compiler/c-linkage.cc

Index: src/compiler/c-linkage.cc
diff --git a/src/compiler/c-linkage.cc b/src/compiler/c-linkage.cc
index 44e0bf1672c374d6451f2b5a0de2b34dbe677a7d..cb47a7228d4e3ad5ba45fb9e5f94ad386a4b8b60 100644
--- a/src/compiler/c-linkage.cc
+++ b/src/compiler/c-linkage.cc
@@ -133,7 +133,7 @@ LinkageLocation regloc(Register reg) {
 
 // General code uses the above configuration data.
 CallDescriptor* Linkage::GetSimplifiedCDescriptor(
-    Zone* zone, const MachineSignature* msig) {
+    Zone* zone, const MachineSignature* msig, bool set_initialize_root_flag) {
   LocationSignature::Builder locations(zone, msig->return_count(),
                                        msig->parameter_count());
 #if 0  // TODO(titzer): instruction selector tests break here.
@@ -220,7 +220,9 @@ CallDescriptor* Linkage::GetSimplifiedCDescriptor(
       Operator::kNoProperties,       // properties
       kCalleeSaveRegisters,          // callee-saved registers
       kCalleeSaveFPRegisters,        // callee-saved fp regs
-      CallDescriptor::kNoFlags,      // flags
+      set_initialize_root_flag ?     // flags
+          CallDescriptor::kInitializeRootRegister
+                               : CallDescriptor::kNoFlags,
       "c-call");
 }