[wasm] Refactor runtime call builders as WasmGraphBuilder members

This is a step towards removing the dependency on CEntryStub. The next
step will reuse BuildCCall to that end. BuildCCall is a member of
WasmGraphBuilder.

Bug: 
Change-Id: I35d3af31b15c04af3d1b877049fd9eccaef306b5
Reviewed-on: https://chromium-review.googlesource.com/549106
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46266}

src/compiler/wasm-compiler.h

@@ -409,6 +409,18 @@ class WasmGraphBuilder {
                         wasm::FunctionSig* sig);
 
   void SetNeedsStackCheck() { needs_stack_check_ = true; }
+
+  //-----------------------------------------------------------------------
+  // Operations involving the CEntryStub, a dependency we want to remove
+  // to get off the GC heap.
+  //-----------------------------------------------------------------------
+  Node* BuildCallToRuntime(Runtime::FunctionId f, Node** parameters,
+                           int parameter_count);
+
+  Node* BuildCallToRuntimeWithContext(Runtime::FunctionId f, Node* context,
+                                      Node** parameters, int parameter_count);
+
+  Node* BuildModifyThreadInWasmFlag(bool new_value);
 };
 
 V8_EXPORT_PRIVATE CallDescriptor* GetWasmCallDescriptor(Zone* zone,