Fix a few more harmless compiler warnings:

- myfree in pager.c was called with an argument, so add one to the
dummy definition
- pgoff is offset_t (unsigned) and doesn't need to be compared to 0
- clang says '*(int *)0 = 0' will be optimized away instead of keeping
the segfault without a volatile hint (?! that is wrong!), but it causes
no harm to add anyway.

arch/x86/kernel/vsyscall.c

@@ -102,7 +102,7 @@ int vsyscall_gettimeofday(struct timeval *tv, void *tz)
 			: "%rcx", "%r11", "memory");
 
 	if (error) {
-		*(int *)0 = 0;	/* i.e. raise(SIGSEGV) */
+		*(volatile int *)0 = 0;	/* i.e. raise(SIGSEGV) */
 	}
 	return error;
 } /* vsyscall_gettimeofday() */