Always include debugger support.

src/x64/macro-assembler-x64.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 273 matching lines @@
   // operation.  RecordWrite filters out smis so it does not update
   // the write barrier if the value is a smi.
   void RecordWrite(
       Register object,
       Register address,
       Register value,
       SaveFPRegsMode save_fp,
       RememberedSetAction remembered_set_action = EMIT_REMEMBERED_SET,
       SmiCheck smi_check = INLINE_SMI_CHECK);
 
-#ifdef ENABLE_DEBUGGER_SUPPORT
   // ---------------------------------------------------------------------------
   // Debugger Support
 
   void DebugBreak();
-#endif
 
   // Generates function and stub prologue code.
   void Prologue(PrologueFrameMode frame_mode);
 
   // Enter specific kind of exit frame; either in normal or
   // debug mode. Expects the number of arguments in register rax and
   // sets up the number of arguments in register rdi and the pointer
   // to the first argument in register rsi.
   //
   // Allocates arg_stack_space * kPointerSize memory (not GCed) on the stack
@@ skipping 1307 matching lines @@
     masm->popfq();                                                           \
   }                                                                          \
   masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_