Use %I64d instead of %lld for MinGW

For older versions of MSVCRT.dll %lld is still using only 32 bits, breaking
32-bit builds defining USE_64_BIT_INT. %I64d is still supported on all newer
MSVCRT.dll releases, so there is really no reason to use %lld with MinGW at
all.

Fixes https://rt.perl.org/Ticket/Display.html?id=120851