g_option_context_parse_strv: use UTF-8 on Windows
g_option_context_parse_strv: use UTF-8 on Windows

Add another difference to the freshly-added g_option_context_parse_strv:
now, on Windows, its arguments on to be in UTF-8 instead of the argv[]
encoding (from the system codepage).

The documentation teases g_win32_get_command_line() which is a new
GLib-filename-encoding-based function that will be added in a following
commit.

https://bugzilla.gnome.org/show_bug.cgi?id=722025

cention-sany/glib,krichter722/glib,lukasz-skalski/glib,gale320/glib,johne53/MB3Glib,MathieuDuponchelle/glib,gale320/glib,gale320/glib,ieei/glib,gale320/glib,krichter722/glib,krichter722/glib,lukasz-skalski/glib,ieei/glib,cention-sany/glib,mzabaluev/glib,tamaskenez/glib,MathieuDuponchelle/glib,mzabaluev/glib,johne53/MB3Glib,johne53/MB3Glib,tamaskenez/glib,cention-sany/glib,tchakabam/glib,cention-sany/glib,ieei/glib,mzabaluev/glib,MathieuDuponchelle/glib,endlessm/glib,mzabaluev/glib,mzabaluev/glib,krichter722/glib,Distrotech/glib,tchakabam/glib,Distrotech/glib,tamaskenez/glib,Distrotech/glib,johne53/MB3Glib,Distrotech/glib,MathieuDuponchelle/glib,Distrotech/glib,lukasz-skalski/glib,endlessm/glib,tchakabam/glib,endlessm/glib,ieei/glib,tamaskenez/glib,lukasz-skalski/glib,krichter722/glib,lukasz-skalski/glib,tchakabam/glib,tchakabam/glib,MathieuDuponchelle/glib,johne53/MB3Glib,endlessm/glib,johne53/MB3Glib,tamaskenez/glib,endlessm/glib,gale320/glib,cention-sany/glib,ieei/glib