Fix missing gettimeofday() declaration.
This avoids a warning under MinGW versions having gettimeofday(), per
buildfarm member walleye.
#include <ctype.h>
#include <limits.h>
+#include <sys/time.h>
#include <time.h>
#ifdef WIN32
#include "win32.h"
#else
#include <unistd.h>
-#include <sys/time.h>
#endif
#include "libpq-fe.h"
