timezone vs _timezone on Windows

I think I see the real issue behind the recent argument about the
datatype of the timezone variable. I don't think the datatype matters,
but the name certainly does. In pgtz.c we have

#if defined(HAVE_STRUCT_TM_TM_ZONE)
return tm->tm_gmtoff;
#elif defined(HAVE_INT_TIMEZONE)
#ifdef HAVE_UNDERSCORE_TIMEZONE
return -_timezone;
#else
return -timezone;
#endif
#else
#error No way to determine TZ? Can this happen?
#endif

but the symbol HAVE_UNDERSCORE_TIMEZONE appears nowhere else ---
certainly it's not set by configure, and never has been. So the
"_timezone" case is dead code at the moment.

In 7.4, pg_config_manual.h contained

/*
* Define this if your operating system has _timezone rather than timezone
*/
#if defined(__CYGWIN__) || defined(WIN32)
#define HAVE_INT_TIMEZONE /* has int _timezone */
#define HAVE_UNDERSCORE_TIMEZONE 1
#endif

but this passage has disappeared from CVS tip. So given a platform that
has "_timezone" but not "timezone", CVS tip is broken.

I am wondering how changing this would affect the existing, allegedly
working Windows port. Should we put back the pg_config_manual.h entry?
Should we restrict it to __CYGWIN__ only?

regards, tom lane