XML backend: build expat XML backend

Adds the expat XML backend to the built files.

clish/shell/module.am

@@ -18,4 +18,6 @@ libclish_la_SOURCES += \
 	clish/shell/private.h \
 	clish/shell/xmlapi.h \
 	clish/shell/shell_roxml.c \
-	clish/shell/shell_libxml2.c
+	clish/shell/shell_libxml2.c \
+	clish/shell/shell_expat.c
+