Add x86_64 to the bionic headers.

Manual changes:

  cpp.py: cope with macros that refer to other macros.

  defaults.py: x86 no longer always implies __i386__; use __i386__ to replace
  the kernel CONFIG_X86_32 flag.

  asm/page.h: the upstream page.h isn't a uapi header and no longer includes
  the stuff we were using it for. Let's just have our own static file, since
  it's the same for all our architectures (both 32- and 64-bit).

  sys/select.h: we used to use the various FD_SET-related macros from the
  kernel header files, but they've gone. Adjust by adding trivial equivalent
  definitions.

Automated changes:

  libc/kernel/arch-x86, libc/kernel/common: regenerated from
  external/kernel-headers.

Change-Id: I84fc0ed52dc742e043b4ae300fd3b58ee99b7fcd
diff --git a/libc/kernel/arch-x86/asm/unistd.h b/libc/kernel/arch-x86/asm/unistd.h
index d109f5f..3e8df69 100644
--- a/libc/kernel/arch-x86/asm/unistd.h
+++ b/libc/kernel/arch-x86/asm/unistd.h
@@ -16,4 +16,16 @@
  ***
  ****************************************************************************
  ****************************************************************************/
-#include "unistd_32.h"
+#ifndef _ASM_X86_UNISTD_H
+#define _ASM_X86_UNISTD_H 1
+#define __X32_SYSCALL_BIT 0x40000000
+#ifdef __i386__
+/* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
+#include <asm/unistd_32.h>
+#elif defined(__ILP32__)
+#include <asm/unistd_x32.h>
+#else
+/* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
+#include <asm/unistd_64.h>
+#endif
+#endif