[gtksourceview] build: include stdlib.h for exit()

[Christian Hergert <chergert src gnome org>]

commit a6b3a7c0ca3253899f00d77766cec5366628fd61
Author: Christian Hergert <chergert redhat com>
Date:   Wed Jan 29 10:12:44 2020 -0800

    build: include stdlib.h for exit()

 testsuite/test-buffer-input-stream.c  | 1 +
 testsuite/test-buffer-output-stream.c | 1 +
 testsuite/test-file-loader.c          | 1 +
 3 files changed, 3 insertions(+)
---
diff --git a/testsuite/test-buffer-input-stream.c b/testsuite/test-buffer-input-stream.c
index f812b522..1ae3cfed 100644
--- a/testsuite/test-buffer-input-stream.c
+++ b/testsuite/test-buffer-input-stream.c
@@ -20,6 +20,7 @@
 
 #include <gio/gio.h>
 #include <gtk/gtk.h>
+#include <stdlib.h>
 #include <string.h>
 #include <gtksourceview/gtksource.h>
 #include "gtksourceview/gtksourcebufferinputstream.h"
diff --git a/testsuite/test-buffer-output-stream.c b/testsuite/test-buffer-output-stream.c
index c844093d..098218f6 100644
--- a/testsuite/test-buffer-output-stream.c
+++ b/testsuite/test-buffer-output-stream.c
@@ -22,6 +22,7 @@
 #include <glib.h>
 #include <glib/gprintf.h>
 #include <gtk/gtk.h>
+#include <stdlib.h>
 #include <string.h>
 #include <gtksourceview/gtksource.h>
 #include "gtksourceview/gtksourcebufferoutputstream.h"
diff --git a/testsuite/test-file-loader.c b/testsuite/test-file-loader.c
index c0b37f18..ee206aba 100644
--- a/testsuite/test-file-loader.c
+++ b/testsuite/test-file-loader.c
@@ -20,6 +20,7 @@
  */
 
 #include <gtksourceview/gtksource.h>
+#include <stdlib.h>
 #include <string.h>
 
 typedef struct