windows: use _strdup() instead of strdup() where missing

[vszakats]

To replace deprecated strdup() CRT calls with the recommended
_strdup().

Refs:
https://learn.microsoft.com/cpp/c-runtime-library/reference/strdup-wcsdup
https://learn.microsoft.com/cpp/c-runtime-library/reference/strdup-wcsdup-mbsdup

[vszakats]

Windows arm64 runs became super flaky today, e.g. here with this one:

--p---oem-- OK (1664 out of 1685, remaining: 00:07, took 5.290s, duration: 10:04)
fopen() failed with error (13) The data is invalid.
Error opening file 'log/3/imap_sockfilt.log'
Msg not logged: 19:37:09.790481 [select_ws] 2972 is readable
exit_signal_handler: failed opening log/3/imap_sockfilt.log
Terminate batch job (Y/N)? 
Error: The action 'run tests' has timed out after 10 minutes.