build: ensure storage driver is used

Commit 1c275e9a accidentally dropped the storage driver from
libvirtd, because it depended on a C preprocessor macro that
was not defined.  Furthermore, if you do './configure
--without-storage-dir --with-storage-disk' or any other combination
where you explicitly build a subset of storage backends excluding
the dir backend, then the build is broken.

Based on analysis by Osier Yang.

* configure.ac (WITH_STORAGE): Define top-level conditional.
* src/Makefile.am (mod_LTLIBRARIES): Build driver even when
storage_dir is disabled.
* daemon/libvirtd.c: Pick up storage driver for any backend, not
just dir.
* daemon/Makefile.am (libvirtd_LDADD): Likewise.

configure.ac

@@ -2076,6 +2076,19 @@ fi
 AC_SUBST([DEVMAPPER_CFLAGS])
 AC_SUBST([DEVMAPPER_LIBS])
 
+with_storage=no
+for backend in dir fs lvm iscsi scsi mpath rbd disk; do
+    if eval test \$with_storage_$backend = yes; then
+        with_storage=yes
+        break
+    fi
+done
+if test $with_storage = yes; then
+    AC_DEFINE([WITH_STORAGE], [1],
+      [Define to 1 if at least one storage backend is in use])
+fi
+AM_CONDITIONAL([WITH_STORAGE], [test "$with_storage" = "yes"])
+
 dnl
 dnl check for libcurl (ESX/XenAPI)
 dnl

daemon/Makefile.am

@@ -140,7 +140,7 @@ if WITH_UML
     libvirtd_LDADD += ../src/libvirt_driver_uml.la
 endif
 
-if WITH_STORAGE_DIR
+if WITH_STORAGE
     libvirtd_LDADD += ../src/libvirt_driver_storage.la
 endif
 

daemon/libvirtd.c

@@ -77,7 +77,7 @@
 # ifdef WITH_NETCF
 #  include "interface/netcf_driver.h"
 # endif
-# ifdef WITH_STORAGE_DIR
+# ifdef WITH_STORAGE
 #  include "storage/storage_driver.h"
 # endif
 # ifdef WITH_NODE_DEVICES
@@ -403,7 +403,7 @@ static void daemonInitialize(void)
 # ifdef WITH_NETCF
     interfaceRegister();
 # endif
-# ifdef WITH_STORAGE_DIR
+# ifdef WITH_STORAGE
     storageRegister();
 # endif
 # ifdef WITH_NODE_DEVICES

src/Makefile.am

@@ -967,7 +967,7 @@ if HAVE_LIBBLKID
 libvirt_driver_storage_la_CFLAGS += $(BLKID_CFLAGS)
 libvirt_driver_storage_la_LIBADD += $(BLKID_LIBS)
 endif
-if WITH_STORAGE_DIR
+if WITH_STORAGE
 if WITH_DRIVER_MODULES
 mod_LTLIBRARIES += libvirt_driver_storage.la
 else