Use the configure support to determine which ndbm.h header to include.
diff --git a/Modules/dbmmodule.c b/Modules/dbmmodule.c
index c0cfb29..afb039b 100644
--- a/Modules/dbmmodule.c
+++ b/Modules/dbmmodule.c
@@ -7,7 +7,17 @@
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
+
+/* Some Linux systems install gdbm/ndbm.h, but not ndbm.h. This supports
+ * whichever configure was able to locate.
+ */
+#if defined(HAVE_NDBM_H)
#include <ndbm.h>
+#elif defined(HAVE_GDBM_NDBM_H)
+#include <gdbm/ndbm.h>
+#else
+#error "No ndbm.h available!"
+#endif
typedef struct {
PyObject_HEAD