capi: Fix regression caused by use of bool data type

Commit 87d33b6 added code which uses bool.
Therefore stdbool.h must be included for compilations with a C compiler.

Signed-off-by: Stefan Weil <[email protected]>

Author: stweil

src/api/capi.h

@@ -30,6 +30,7 @@
 #   include "renderer.h"
 #else
 #   include "platform.h"
+#   include <stdbool.h>
 #   include <stdio.h>
 #endif