9pfs: improve portability to older systems

Small requirements on "new" features have percolated to virtio-9p-local.c.
In particular, the utimensat wrapper actually only supports dirfd = AT_FDCWD
and flags = AT_SYMLINK_NOFOLLOW in the fallback code.  Remove the arguments
so that virtio-9p-local.c will not use AT_* constants.

At the same time, fail local_ioc_getversion if the ioctl is not supported
by the host.

Signed-off-by: Paolo Bonzini <[email protected]>
Signed-off-by: Anthony Liguori <[email protected]>
diff --git a/qemu-os-posix.h b/qemu-os-posix.h
index 920499d..8e1149d 100644
--- a/qemu-os-posix.h
+++ b/qemu-os-posix.h
@@ -44,7 +44,6 @@
 #endif
 #endif
 typedef struct timespec qemu_timespec;
-int qemu_utimensat(int dirfd, const char *path, const qemu_timespec *times,
-    int flags);
+int qemu_utimens(const char *path, const qemu_timespec *times);
 
 #endif