Fix x86_64 register names in <sys/user.h>.

Change-Id: Ieb327247a41f6195589716170e324d1cd1251b96
diff --git a/libc/include/sys/user.h b/libc/include/sys/user.h
index 1a25ac1..bf762e7 100644
--- a/libc/include/sys/user.h
+++ b/libc/include/sys/user.h
@@ -117,22 +117,22 @@
   unsigned long r14;
   unsigned long r13;
   unsigned long r12;
-  unsigned long bp;
-  unsigned long bx;
+  unsigned long rbp;
+  unsigned long rbx;
   unsigned long r11;
   unsigned long r10;
   unsigned long r9;
   unsigned long r8;
-  unsigned long ax;
-  unsigned long cx;
-  unsigned long dx;
-  unsigned long si;
-  unsigned long di;
-  unsigned long orig_ax;
-  unsigned long ip;
+  unsigned long rax;
+  unsigned long rcx;
+  unsigned long rdx;
+  unsigned long rsi;
+  unsigned long rdi;
+  unsigned long orig_rax;
+  unsigned long rip;
   unsigned long cs;
-  unsigned long flags;
-  unsigned long sp;
+  unsigned long eflags;
+  unsigned long rsp;
   unsigned long ss;
   unsigned long fs_base;
   unsigned long gs_base;