MinGW: fix error of undefined strcmp() (#2837)

diff --git a/contrib/gdk-pixbuf/loader.c b/contrib/gdk-pixbuf/loader.c
index 8a8180a..27b08d8 100644
--- a/contrib/gdk-pixbuf/loader.c
+++ b/contrib/gdk-pixbuf/loader.c
@@ -4,6 +4,7 @@
 
 #include <avif/avif.h>
 #include <stdlib.h>
+#include <string.h>
 
 #define GDK_PIXBUF_ENABLE_BACKEND
 #include <gdk-pixbuf/gdk-pixbuf-io.h>