MinGW does not provide comsupp.lib, so there's no implementation of
_com_util::ConvertBSTRToString. Use a fallback implementation that
uses wcstombs() instead.
On MinGW we also truncate the name to 100 chars which should be fine.
"meson encountered an error in file
sys/decklink/meson.build, line 33, column 2:
Invalid use of addition: must be str, not list"
Also remove nonsensical linker flags on windows.
https://bugzilla.gnome.org/show_bug.cgi?id=781156
