Value is not set for a constant if it's defined as the value of another constant.

[WoodyGuo]

In the following IDL file, there are 4 constants defined: days_7, days_14, days_30, and days_default.
The days_default and the days_30 are having the same value.

`interface_xxx = interface +c {

const days_7: i8 = 7;
const days_14: i8 = 14;
const days_30: i8 = 30;
const days_default: i8 = days_30;

}`

Compilation will fail after generating the code using the IDL file above, complaining with error "declaration of constexpr static data member 'DAYS_DEFAULT' requires an initializer".

Contents of the header and implementations files generated are listed below:

`
// interface_xxx.h
class InterfaceXxx {
public:
virtual ~InterfaceXxx() {}

static constexpr int8_t DAYS_7 = 7;
static constexpr int8_t DAYS_14 = 14;
static constexpr int8_t DAYS_30 = 30;
static constexpr int8_t DAYS_DEFAULT;
}`

`
// interface_xxx.cc
namespace ns {

int8_t const InterfaceXxx::DAYS_7;
int8_t const InterfaceXxx::DAYS_14;
int8_t const InterfaceXxx::DAYS_30;
int8_t const InterfaceXxx::DAYS_DEFAULT;

}`

[artwyman]

Note from prior discussion elsewhere: Looks likely to have been introduced by #354