GLib: Add forgotten includes and build fixes

GLib: Add forgotten includes and build fixes

-gcharset.c, genviron.c, gunicollate.c: Some headers were missed in those
 files that triggered C4013 warnings/errors (aka. implicit declaration
 of ... in GCC).  Make up for them here.
-gwin32.h: Only define g_win32_get_package_installation_directory/
 g_win32_get_package_installation_subdirectory as macros
 (alias of g_win32_get_package_installation_directory_utf8/
 g_win32_get_package_installation_subdirectory_utf8) on Win64 (x64) as
 g_win32_get_package_installation_directory/
 g_win32_get_package_installation_subdirectory have seperate existing
 implmentations for Win32-this is a long-standing problem but was covered-
 up by G_DISABLE_DEPRECATED, which we are stopping to use as of 2.31.0.