[gegl] tools: include string.h for strlen

[Øyvind "pippin" Kolås <ok src gnome org>]

commit 57582a25eb89e37806526b883566e3666e144e8d
Author: Øyvind Kolås <pippin gimp org>
Date:   Mon Apr 1 00:30:12 2019 +0200

    tools: include string.h for strlen

 tools/exp_combine.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/tools/exp_combine.cpp b/tools/exp_combine.cpp
index c74f81cf6..6fd0df04c 100644
--- a/tools/exp_combine.cpp
+++ b/tools/exp_combine.cpp
@@ -5,7 +5,7 @@
 #include <cstdio>
 #include <cerrno>
 #include <cmath>
-
+#include <string.h>
 #include <iostream>
 
 #include <gexiv2/gexiv2.h>