core: fix compilation on Cygwin

The header sys/select.h is now required for select() function.

src/core/wee-hook.c

@@ -32,6 +32,7 @@
 #include <time.h>
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <sys/select.h>
 #include <signal.h>
 #include <fcntl.h>
 #include <errno.h>

src/core/wee-network.c

@@ -39,6 +39,7 @@
 #include <string.h>
 #include <sys/types.h>
 #include <sys/socket.h>
+#include <sys/select.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <netdb.h>

src/gui/curses/gui-curses-main.c

@@ -29,6 +29,7 @@
 #include <string.h>
 #include <signal.h>
 #include <time.h>
+#include <sys/select.h>
 
 #include "../../core/weechat.h"
 #include "../../core/wee-command.h"