Wrongly assumes that futex_waitv is missing if no glibc-only __NR_futex_waitv.
https://bugs.gentoo.org/868747
--- a/configure.ac
+++ b/configure.ac
@@ -2153,2 +2153,5 @@
 
+dnl Check for futex_waitv structure members
+AC_CHECK_MEMBERS(struct futex_waitv.val,,,[#include <linux/futex.h>])
+
 dnl Check for socket structure members
--- a/dlls/ntdll/unix/fsync.c
+++ b/dlls/ntdll/unix/fsync.c
@@ -67,2 +67,4 @@
 # define __NR_futex_waitv 449
+#endif
+#ifndef HAVE_STRUCT_FUTEX_WAITV_VAL
 # define FUTEX_32 2