Add arch-x86_64/include/machine.

This is basically the other half of I5de76f6c46ac87779f207d568a86bb453e2414de
from Pavel Chupin <pavel.v.chupin@intel.com>, but taking the exact upstream
_types.h instead of the modified version. (I was confused when I suggested
otherwise.)

I've also cleaned up the internal_types.h situation; we weren't gaining
anything from these empty files, and there is no upstream internal_types.h
for x86_64.

Change-Id: I802a9a6a8df1c979e820659212c75a47c2ef392e

libc/include/sys/limits.h

@@ -31,18 +31,6 @@
 
 /* Common definitions for limits.h. */
 
-/*
- * <machine/internal_types.h> is meant to describe a specific architecture,
- * but to be a safe include, that doesn't ever define anything that is
- * user-visible (only typedefs and #define names that stays in the __xxx
- * namespace).
- *
- *   __machine_has_unsigned_chars	(default is signed chars)
- *   __FLT_xxx/__DBL_xxx		non standard values for floating
- *   					points limits.
- */
-#include <machine/internal_types.h>
-
 /* Legacy */
 #include <machine/limits.h>
 
@@ -52,7 +40,7 @@
 #define SCHAR_MIN	(-0x7f-1)	/* min value for a signed char */
 
 #define	UCHAR_MAX	0xffU		/* max value for an unsigned char */
-#ifdef __machine_has_unsigned_chars
+#ifdef __CHAR_UNSIGNED__
 # define CHAR_MIN	0		/* min value for a char */
 # define CHAR_MAX	0xff		/* max value for a char */
 #else