build: Add libcurl dependency to libvirt_driver.la

libvirt.c calls curl_global_init() if WITH_CURL is defined and thus it
should be linked with libcurl. This fixes link failure in case neither
xenapi nor esx driver is enabled (they are the only users of libcurl).
(cherry picked from commit 514b9306)

src/Makefile.am

@@ -792,9 +792,11 @@ noinst_LTLIBRARIES += libvirt_driver.la
 libvirt_la_BUILT_LIBADD += libvirt_driver.la
 libvirt_driver_la_SOURCES = $(DRIVER_SOURCES)
 
-libvirt_driver_la_CFLAGS = $(NUMACTL_CFLAGS) $(GNUTLS_CFLAGS) \
+libvirt_driver_la_CFLAGS = \
+		$(NUMACTL_CFLAGS) $(GNUTLS_CFLAGS) $(CURL_CFLAGS) \
 		-I$(top_srcdir)/src/conf $(AM_CFLAGS)
-libvirt_driver_la_LIBADD = $(NUMACTL_LIBS) $(GNUTLS_LIBS) $(DLOPEN_LIBS)
+libvirt_driver_la_LIBADD = \
+		$(NUMACTL_LIBS) $(GNUTLS_LIBS) $(CURL_LIBS) $(DLOPEN_LIBS)
 
 USED_SYM_FILES = $(srcdir)/libvirt_private.syms