If last character in command is ampersand, do not use my_popen/my_pclose
in "exec", instead do CreateProcess() without a window.
The effect of this is background execution of exec command, ampersand is chosen as to emulate to Unix shell behavior.
Background execution had been already used in a test, which so far exclude Windows, see 10.5+ mysql-test/main/shutdown_not_windows.inc
There is another special case
MDEV-26713, we want to start a server, with Unicode command line, and with characters outside of current ANSI codepage, e.g for the datadir . Normally, one could use MTR's "restart" functionality which would launch process via mysql-test-run.pl, i.e from Perl.
But in this case, perl shows an i18n deficiency - Unicode would get lost/replaced with question marks.
As a workaround for Perl deficiency, "exec $MYSQLD.. &" can be used.