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:
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)