vhost: fix C++ include

[ upstream commit 1d1126a ]

The virtio kernel header includes are already noted as being
incompatible with C++. We can ensure that the header is safe for
inclusion in C++ code by not including those headers during C++ builds.
While not ideal, this does ensure that all DPDK headers can be included
in C++ code without errors.

Fixes: f8904d5 ("vhost: fix header for strict compilation flags")

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>

lib/librte_vhost/rte_vhost.h

@@ -21,10 +21,12 @@
 extern "C" {
 #endif
 
+#ifndef __cplusplus
 /* These are not C++-aware. */
 #include <linux/vhost.h>
 #include <linux/virtio_ring.h>
 #include <linux/virtio_net.h>
+#endif
 
 #define RTE_VHOST_USER_CLIENT		(1ULL << 0)
 #define RTE_VHOST_USER_NO_RECONNECT	(1ULL << 1)