screenshooter: Only link to $(CLIENT_LIBS) not libtoytoolkit.la

This application doesn't use toytoolkit, so don't link to it.  We have to
add a copy of xmalloc, to link without toytoolkit.
diff --git a/clients/screenshot.c b/clients/screenshot.c
index d58d8b1..1c0f203 100644
--- a/clients/screenshot.c
+++ b/clients/screenshot.c
@@ -20,7 +20,10 @@
  * OF THIS SOFTWARE.
  */
 
+#include "config.h"
+
 #include <stdint.h>
+#include <errno.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
@@ -75,6 +78,21 @@
 	}
 }
 
+static void *
+xmalloc(size_t size)
+{
+	void *p;
+
+	p = malloc(size);
+	if (p == NULL) {
+		fprintf(stderr, "%s: out of memory\n",
+			program_invocation_short_name);
+		exit(EXIT_FAILURE);
+	}
+
+	return p;
+}
+
 static void
 display_handle_mode(void *data,
 		    struct wl_output *wl_output,
@@ -185,7 +203,7 @@
 
 	buffer_stride = width * 4;
 
-	data = malloc(buffer_stride * height);
+	data = xmalloc(buffer_stride * height);
 	if (!data)
 		return;