extconf.rb in duckdb-0.0.6

- old
+ new

@@ -1,5 +1,7 @@
 require 'mkmf'
 
 dir_config('duckdb')
-have_library('duckdb')
-create_makefile('duckdb/duckdb_native')
+if have_library('duckdb')
+  have_func('duckdb_bind_null', 'duckdb.h')
+  create_makefile('duckdb/duckdb_native')
+end