Use sys/uio.h for writev()

With glibc >= 2.25.90 writev() is only available if you explicitly
include sys/uio.h. This matches the documented requirements, but
older glibc and other *NIX pulled in writev indirectly so the bug
wasn't noticed previously.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/util/virlog.c

@@ -32,6 +32,7 @@
 #include <unistd.h>
 #include <execinfo.h>
 #include <regex.h>
+#include <sys/uio.h>
 #if HAVE_SYSLOG_H
 # include <syslog.h>
 #endif