remove most uses of Isolate::Current in arch specific files

src/x64/regexp-macro-assembler-x64.cc

 // 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 1170 matching lines @@
 template <typename T>
 static T& frame_entry(Address re_frame, int frame_offset) {
   return reinterpret_cast<T&>(Memory::int32_at(re_frame + frame_offset));
 }
 
 
 int RegExpMacroAssemblerX64::CheckStackGuardState(Address* return_address,
                                                   Code* re_code,
                                                   Address re_frame) {
   Isolate* isolate = frame_entry<Isolate*>(re_frame, kIsolate);
-  ASSERT(isolate == Isolate::Current());
   if (isolate->stack_guard()->IsStackOverflow()) {
     isolate->StackOverflow();
     return EXCEPTION;
   }
 
   // If not real stack overflow the stack guard was used to interrupt
   // execution for another purpose.
 
   // If this is a direct call from JavaScript retry the RegExp forcing the call
   // through the runtime system. Currently the direct call cannot handle a GC.
@@ skipping 238 matching lines @@
   }
 }
 
 #undef __
 
 #endif  // V8_INTERPRETED_REGEXP
 
 }}  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64