We must link to ws2_32.lib for all Windows builds, and we need to use
workarounds for alloca() and snprintf() since Visual Studio uses
_alloca() for alloca() and provides snprintf() only on Visual Studio
2015 or later, meaning that we need to use _snprintf() here.
Also fix the parts where we run the Python scripts to generate items,
since those scripts already have shebang lines for Meson to pick up.
libicu is an internal dependency of libpsl, so if an executable
uses libicu directly, linking on libpsl is not enough, it must also
link on libicu.
Closes: #115