I have been having a problem with unexpected status returns from calls
to isc_dsql_prepare etc.

I think the problem is due to the definition of ISC_STATUS.

In ibase.h it is defined like this:

typedef intptr_t ISC_STATUS;

Where intptr_t is defined like this:

#if defined(_WIN64)
typedef __int64 intptr_t;
typedef unsigned __int64 uintptr_t;
#else
typedef long intptr_t;
typedef unsigned long uintptr_t;
#endif
#endif

But MinGW-W64 does not define _WIN64, so intptr_t is not typedef'd
correctly.

Therefore I think the first line should instead be:

#if defined(_WIN64) || defined (__x86_64__)

I couldn't find this mentioned anywhere, but sorry if my searching was
not sufficient.