path separator for mingw

path separator in glib2 depends on OS being windows "" or linux "/"

https://gitlab.gnome.org/GNOME/glib/-/blob/master/meson.build#L1458

but there's a mixing OS "mingw" where you're on windows, but your paths are like linux.

I see win32unix out there to deal with this:

https://github.com/albfan/ag.vim/commit/d2c4e5cbdf4852550811857e3038ea7a432c3264#diff-127e60fb2c915764cf9aaa367cec71c31f889bb3abb37c716e711ec8d5cc2b5aR45

Is possible to detect this mixed OS system on meson and build glib2 on msys that way?

This is hitting gitg on windows (which is build on mingw) gitg#66 (moved)