[gtk: 4/8] Fix compilation with clang

[Luca Bacci <lbacci src gnome org>]

commit 0fdf2cc1955b27dabeb25965baabdb994a2ef2f5
Author: Luca Bacci <luca bacci982 gmail com>
Date:   Sun Jan 2 18:22:18 2022 +0100

    Fix compilation with clang
    
    From https://github.com/msys2/MINGW-packages/pull/9509

 gtk/gtklabel.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/gtk/gtklabel.c b/gtk/gtklabel.c
index e0f5565b84..c2a108aab3 100644
--- a/gtk/gtklabel.c
+++ b/gtk/gtklabel.c
@@ -55,6 +55,7 @@
 #include "gtkjoinedmenuprivate.h"
 
 #include <math.h>
+#include <stdlib.h>
 #include <string.h>
 
 /**