Fixes for C enums used in an API and the definition of the enum has not been parsed.

For D, this fixes a segfault in SWIG.

Java, C#, D, Go now produce code that compiles, although the definition of the
enum is needed in order to use the enum properly from the target language.

Examples/test-suite/common.mk

@@ -580,6 +580,7 @@ C_TEST_CASES += \
 	enums \
 	enum_forward \
 	enum_macro \
+	enum_missing \
 	extern_declaration \
 	funcptr \
 	function_typedef \