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

libc/kernel/tools/cpp.py

@@ -1345,7 +1345,11 @@ class CppExpr:
                 if macros[name] == kCppUndefinedMacro:
                     return ("int", 0)
                 else:
-                    return ("int", 1)
+                    try:
+                        value = int(macros[name])
+                        return ("int", value)
+                    except:
+                        return ("defined", macros[name])
 
             if kernel_remove_config_macros and name.startswith("CONFIG_"):
                 return ("int", 0)