use consistent guards for off_t and size_t defines for IA

Change-Id: Ie92b7597883c99e7f4101f4cf5e0ad267b4ee706
diff --git a/libc/arch-x86/include/machine/_types.h b/libc/arch-x86/include/machine/_types.h
index be4f6e4..e9280a5 100644
--- a/libc/arch-x86/include/machine/_types.h
+++ b/libc/arch-x86/include/machine/_types.h
@@ -36,8 +36,8 @@
 #define _I386__TYPES_H_
 
 /* the kernel defines size_t as unsigned int, but g++ wants it to be unsigned long */
-#ifndef _SIZE_T
-#  define _SIZE_T
+#ifndef _SIZE_T_DEFINED_
+#  define _SIZE_T_DEFINED_
 #  ifdef ANDROID
      typedef unsigned int  size_t;
 #  else
@@ -54,9 +54,6 @@
 typedef long           ptrdiff_t;
 #endif
 
-#define _OFF_T_DEFINED_
-#define _SIZE_T_DEFINED_
-
 #include <linux/types.h>
 
 /* 7.18.1.1 Exact-width integer types */