build: fix FreeBSD build

Commit 7c9a2d88 cleaned up too many headers; FreeBSD builds
failed due to:

util/virutil.c:556: warning: implicit declaration of function 'canonicalize_file_name'

(Not sure which Linux header leaked this declaration, but gnulib
only guarantees it in stdlib.h)

libvirt.c:956: warning: implicit declaration of function 'virGetUserConfigDirectory'

(Here, a build on Linux was picking up virutil.h indirectly via
one of the conditional driver headers, where that driver was not
being built on my FreeBSD setup)

* src/util/virutil.c (includes): Need <stdlib.h> for
canonicalize_file_name.
* src/libvirt.c (includes): Use "virutil.h" unconditionally,
rather than relying on conditional indirect inclusion.
Signed-off-by: NEric Blake <eblake@redhat.com>

src/libvirt.c

@@ -63,6 +63,7 @@
 #include "viruri.h"
 #include "virthread.h"
 #include "virstring.h"
+#include "virutil.h"
 
 #ifdef WITH_TEST
 # include "test/test_driver.h"

src/util/virutil.c

@@ -29,6 +29,7 @@
 #include <dirent.h>
 #include <stdio.h>
 #include <stdarg.h>
+#include <stdlib.h>
 #include <unistd.h>
 #include <fcntl.h>
 #include <errno.h>