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
diff --git a/libc/arch-x86_64/include/machine/cdefs.h b/libc/arch-x86_64/include/machine/cdefs.h
new file mode 100644
index 0000000..eb243a3
--- /dev/null
+++ b/libc/arch-x86_64/include/machine/cdefs.h
@@ -0,0 +1,21 @@
+/*	$OpenBSD: cdefs.h,v 1.3 2013/03/28 17:30:45 martynas Exp $	*/
+
+/*
+ * Written by J.T. Conklin <jtc@wimsey.com> 01/17/95.
+ * Public domain.
+ */
+
+#ifndef	_MACHINE_CDEFS_H_
+#define	_MACHINE_CDEFS_H_
+
+#define __strong_alias(alias,sym)					\
+	__asm__(".global " __STRING(alias) " ; " __STRING(alias)	\
+	    " = " __STRING(sym))
+#define __weak_alias(alias,sym)						\
+	__asm__(".weak " __STRING(alias) " ; " __STRING(alias)		\
+	    " = " __STRING(sym))
+#define __warn_references(sym,msg)					\
+	__asm__(".section .gnu.warning." __STRING(sym)			\
+	    " ; .ascii \"" msg "\" ; .text")
+
+#endif /* !_MACHINE_CDEFS_H_ */