`ACE_OS::fstat` doesn't seem to work on MinGW

[iguessthislldo]

Issue came up as part of CI testing of https://github.com/DOCGroup/ACE_TAO/pull/1783

In the PR the following code was added to tao_idl:

https://github.com/DOCGroup/ACE_TAO/blob/f86b6106d9a4d122555a47e860b7f83284d4a31b/TAO/TAO_IDL/driver/drv_preproc.cpp#L1194-L1229

Link to CI run:

https://github.com/DOCGroup/ACE_TAO/runs/5153727424?check_suite_focus=true

If link is no longer valid, error was:

D:\a\ACE_TAO\ACE_TAO\ACE\bin\tao_idl.exe: ERROR: Unable to open file (fstat) "IOP_Codec.pidl": No such device or address

The configuration for the CI in question at the time of running was defined here.