Fix compile error when curl is not used

Noticed in my PowerPC Linux VM:

    cc1: warnings being treated as errors
    dload.c:45: error: 'get_filename' defined but not used
    make[3]: *** [dload.lo] Error 1

Signed-off-by: Dan McGee <dan@archlinux.org>

lib/libalpm/dload.c

@@ -42,6 +42,9 @@
 #include "util.h"
 #include "handle.h"
 
+#ifdef HAVE_LIBCURL
+static double prevprogress; /* last download amount */
+
 static const char *get_filename(const char *url)
 {
 	char *filename = strrchr(url, '/');
@@ -51,9 +54,6 @@ static const char *get_filename(const char *url)
 	return filename;
 }
 
-#ifdef HAVE_LIBCURL
-static double prevprogress; /* last download amount */
-
 static char *get_fullpath(const char *path, const char *filename,
 		const char *suffix)
 {