make x86_64 struct utmp glibc-compatible

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

libc/sysdeps/linux/x86_64/bits/wordsize.h

@@ -2,7 +2,8 @@
 
 #if defined __x86_64__
 # define __WORDSIZE	64
-/*# define __WORDSIZE_COMPAT32	1*/
+/* This makes /var/run/utmp compatible with 32-bit environment: */
+# define __WORDSIZE_COMPAT32	1
 #else
 # define __WORDSIZE	32
 #endif