virtio-9p: fix build on !CONFIG_UTIMENSAT

This patch introduce a fallback mechanism for old systems that do not
support utimensat().  This fix build failure with following warnings:

hw/virtio-9p-local.c: In function 'local_utimensat':
hw/virtio-9p-local.c:479: warning: implicit declaration of function 'utimensat'
hw/virtio-9p-local.c:479: warning: nested extern declaration of 'utimensat'

and:

hw/virtio-9p.c: In function 'v9fs_setattr_post_chmod':
hw/virtio-9p.c:1410: error: 'UTIME_NOW' undeclared (first use in this function)
hw/virtio-9p.c:1410: error: (Each undeclared identifier is reported only once
hw/virtio-9p.c:1410: error: for each function it appears in.)
hw/virtio-9p.c:1413: error: 'UTIME_OMIT' undeclared (first use in this function)
hw/virtio-9p.c: In function 'v9fs_wstat_post_chmod':
hw/virtio-9p.c:2905: error: 'UTIME_OMIT' undeclared (first use in this function)

[NOTE: At this time virtio-9p is only user of utimensat(), and is available
       only when host is linux and CONFIG_VIRTFS is defined.  So there are
       no similar warning for win32.  Please provide a wrapper for win32 in
       oslib-win32.c if new user really requires it.]

v5:
  - Allow fallback on runtime
  - Move qemu_utimensat() to oslib-posix.c
  - Rebased on latest qemu.git
v4:
  - Use tv_now.tv_usec
v3:
  - Use better alternative handling for UTIME_NOW/OMIT
  - Move qemu_utimensat() to cutils.c
V2:
  - Introduce qemu_utimensat()

Acked-by: Chris Wright <[email protected]>
Acked-by: M. Mohan Kumar <[email protected]>
Acked-by: Jes Sorensen <[email protected]>
Signed-off-by: Hidetoshi Seto <[email protected]>
Signed-off-by: Venkateswararao Jujjuri <[email protected]>
diff --git a/qemu-os-posix.h b/qemu-os-posix.h
index 353f878..81fd9ab 100644
--- a/qemu-os-posix.h
+++ b/qemu-os-posix.h
@@ -39,4 +39,16 @@
 typedef struct timeval qemu_timeval;
 #define qemu_gettimeofday(tp) gettimeofday(tp, NULL)
 
+#ifndef CONFIG_UTIMENSAT
+#ifndef UTIME_NOW
+# define UTIME_NOW     ((1l << 30) - 1l)
+#endif
+#ifndef UTIME_OMIT
+# define UTIME_OMIT    ((1l << 30) - 2l)
+#endif
+#endif
+typedef struct timespec qemu_timespec;
+int qemu_utimensat(int dirfd, const char *path, const qemu_timespec *times,
+    int flags);
+
 #endif