Don't import loop.h unless HAVE_DECL_LO_FLAGS_AUTOCLEAR is defined

The loop.h on RHEL4 is broken and cannot be imported. We already
detect this in configure as a side-effect of looking for whether
LO_FLAGS_AUTOCLEAR is available. We protected the impl with
HAVE_DECL_LO_FLAGS_AUTOCLEAR, but not the header import
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/util/virfile.c

@@ -32,7 +32,7 @@
 #include <unistd.h>
 #include <dirent.h>
 
-#ifdef __linux__
+#if defined(__linux__) && HAVE_DECL_LO_FLAGS_AUTOCLEAR
 # include <linux/loop.h>
 # include <sys/ioctl.h>
 #endif