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() */

kernel/pager.c

@@ -161,7 +161,7 @@ myalloc(struct swapinfo *si, size_t sz)
 }
 
 void
-myfree()
+myfree(void *p)
 {
 	/* nothing so far */
 }

kernel/syscall.c

@@ -7589,7 +7589,7 @@ SYSCALL_DECLARE(remap_file_pages)
 	ihk_mc_spinlock_lock_noirq(&thread->vm->memory_range_lock);
 #define	PGOFF_LIMIT	((off_t)1 << ((8*sizeof(off_t) - 1) - PAGE_SHIFT))
 	if ((size <= 0) || (size & (PAGE_SIZE - 1)) || (prot != 0)
-			|| (pgoff < 0) || (PGOFF_LIMIT <= pgoff)
+			|| (PGOFF_LIMIT <= pgoff)
 			|| ((PGOFF_LIMIT - pgoff) < (size / PAGE_SIZE))
 			|| !((start < end) || (end == 0))) {
 		ekprintf("sys_remap_file_pages(%#lx,%#lx,%#x,%#lx,%#x):"