VM: Use constant pool also for leaf runtime calls on x64, arm, arm64 and mips.

runtime/vm/assembler_x64.h

Index: runtime/vm/assembler_x64.h
diff --git a/runtime/vm/assembler_x64.h b/runtime/vm/assembler_x64.h
index 3dab1ccd84a886f39891f875c4235e7dbf3e69bf..5cb3c177044d977de426fa2bc85c2682cdefb770 100644
--- a/runtime/vm/assembler_x64.h
+++ b/runtime/vm/assembler_x64.h
@@ -686,7 +686,6 @@ class Assembler : public ValueObject {
 
   // Note: verified_mem mode forces far jumps.
   void j(Condition condition, Label* label, bool near = kFarJump);
-  void j(Condition condition, const ExternalLabel* label);
 
   void jmp(Register reg);
   void jmp(const Address& address);
@@ -767,15 +766,10 @@ class Assembler : public ValueObject {
   void LoadFunctionFromCalleePool(Register dst,
                                   const Function& function,
                                   Register new_pp);
-  void JmpPatchable(const ExternalLabel* label, Register pp);
   void JmpPatchable(const StubEntry& stub_entry, Register pp);
-  void Jmp(const ExternalLabel* label, Register pp);
   void Jmp(const StubEntry& stub_entry, Register pp);
-  void J(Condition condition, const ExternalLabel* label, Register pp);
   void J(Condition condition, const StubEntry& stub_entry, Register pp);
-  void CallPatchable(const ExternalLabel* label);
   void CallPatchable(const StubEntry& stub_entry);
-  void Call(const ExternalLabel* label);
   void Call(const StubEntry& stub_entry);
   // Unaware of write barrier (use StoreInto* methods for storing to objects).
   // TODO(koda): Add StackAddress/HeapAddress types to prevent misuse.
@@ -849,7 +843,6 @@ class Assembler : public ValueObject {
 
   // Call runtime function. Reserves shadow space on the stack before calling
   // if platform ABI requires that. Does not restore RSP after the call itself.
-  void CallCFunction(const ExternalLabel* label);
   void CallCFunction(Register reg);
 
   /*