Move the include directive to the enum template

There is no actual written guarantee in glib-mkenums that the template
line specified using --fhead will be added after the templates specified
inside the template file. Since the template file is only used once, we
can simply move the `#include` directive inside the template, so that it
is guaranteed to be in the right place.

Closes: #1007
Approved by: cgwalters

src/libostree/ostree-enumtypes.c.template

@@ -23,6 +23,8 @@
 #endif
 #include <string.h>
 
+#include "ostree-enumtypes.h"
+
 /*** END file-header ***/
 
 /*** BEGIN file-production ***/