[Libvir] Build error without Xen

Hi, The recent changes to src/xml.c breaks the build without xen: $ ./autogen.sh \ --prefix=/usr \ --mandir=\${prefix}/share/man \ --infodir=\${prefix}/share/info \ --sysconfdir=/etc \ --localstatedir=/var \ --without-xen $ make ... gcc -g -O2 -o .libs/virsh -Wall -Wmissing-prototypes -Wnested-externs -Wpointer-arith -Wextra -Wshadow -Wcast-align -Wwrite-strings -Waggregate-return -Wstrict-prototypes -Winline -Wredundant-decls -Wno-sign-compare -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fasynchronous-unwind-tables virsh-virsh.o virsh-console.o -Wall -Wmissing-prototypes -Wnested-externs -Wpointer-arith -Wextra -Wshadow -Wcast-align -Wwrite-strings -Waggregate-return -Wstrict-prototypes -Winline -Wredundant-decls -Wno-sign-compare -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fasynchronous-unwind-tables ./.libs/libvirt.so -lcurses -lreadline ./.libs/libvirt.so: undefined reference to `xenNbCpus' collect2: ld returned 1 exit status make[2]: *** [virsh] Error 1 make[2]: Leaving directory `/usr/local/src/libvirt/libvirt/src' -jim