Avoid writing the sandbox base address to memory in setjmp and memcpy

newlib/libc/machine/x86_64/x86_64mach.h

 /*
  ** This file is distributed WITHOUT ANY WARRANTY; without even the implied
  ** warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  */
 
 #ifndef __USER_LABEL_PREFIX__
 #define __USER_LABEL_PREFIX__ _
 #endif
 
 #define __REG_PREFIX__ %
@@ skipping 40 matching lines @@
 
 #define r8d  REG(r8d)
 #define r9d  REG(r9d)
 #define r10d REG(r10d)
 #define r11d REG(r11d)
 #define r12d REG(r12d)
 #define r13d REG(r13d)
 #define r14d REG(r14d)
 #define r15d REG(r15d)
 
+#define r8b  REG(r8b)
+
 #define st0 REG(st)
 #define st1 REG(st(1))
 #define st2 REG(st(2))
 #define st3 REG(st(3))
 #define st4 REG(st(4))
 #define st5 REG(st(5))
 #define st6 REG(st(6))
 #define st7 REG(st(7))
 
 #define ax REG(ax)
@@ skipping 42 matching lines @@
 #define SOTYPE_FUNCTION(sym)
 #endif
 
 #ifdef _I386MACH_ALLOW_HW_INTERRUPTS
 #define        __CLI
 #define        __STI
 #else
 #define __CLI  cli
 #define __STI  sti
 #endif