A64: Let the MacroAssembler resolve branches to distant targets.

src/a64/assembler-a64-inl.h

Index: src/a64/assembler-a64-inl.h
diff --git a/src/a64/assembler-a64-inl.h b/src/a64/assembler-a64-inl.h
index ebd3ec8b4d919b4e2212aefa5aa5fe919dd6ebc8..30e140a2cd211318197a73e43a8e0a80e00e676d 100644
--- a/src/a64/assembler-a64-inl.h
+++ b/src/a64/assembler-a64-inl.h
@@ -493,6 +493,16 @@ Operand MemOperand::OffsetAsOperand() const {
 }
 
 
+void Assembler::Unreachable() {
+#ifdef USE_SIMULATOR
+  debug("UNREACHABLE", __LINE__, BREAK);
+#else
+  // Crash by branching to 0. lr now points near the fault.
+  Emit(BLR | Rn(xzr));
+#endif
+}
+
+
 Address Assembler::target_pointer_address_at(Address pc) {
   Instruction* instr = reinterpret_cast<Instruction*>(pc);
   ASSERT(instr->IsLdrLiteralX());