Add a few missing includes, caught while compiling on cygwin

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

lib/libalpm/util.h

@@ -26,6 +26,7 @@
 #define _ALPM_UTIL_H
 
 #include <stdio.h>
+#include <stdarg.h>
 #include <libintl.h> /* here so it doesn't need to be included elsewhere */
 #include <time.h>
 

src/pacman/util.c

@@ -34,6 +34,7 @@
 #include <ctype.h>
 #include <dirent.h>
 #include <unistd.h>
+#include <limits.h>
 
 #include <alpm.h>
 #include <alpm_list.h>