workaround for MS Windows' insanity (ignores partition types / hidden flag since 2018)

[Marcel Partap]

Dear grub devs,
as we have just last week released a hundred of our debian-based 
https://github.com/fsfw-dresden/usb-live-linux/ sticks .. and at the moment are 
rolling out a version for primary schools, I have stumbled over the pure 
stupidity that is Windows 10's handling of partitioned usb drives. As seems 
abundantly documented, windows changed its behaviour sometime last year and now 
blatantly ignores the hidden flag, displaying partitions regardless of type and 
prominently offering to format non-windows filesystems. I was somewhat shocked 
at this ridiculous demeanour.. After an hour of investigating this I found the 
very sole workaround was to set the partition type to 0 - empty/none. This was 
the only way to windows not show and offer to format partitions beyond the 
exchange FAT partition. Rejoicing, on restart I found out that grub would not 
proceed booting from a partition of type "empty". Now semantically, that is 
totally correct. However, in order to provide us with a coping mechanism for 
such live linux use scenarios, I propose to add a flag that overrides this code:
>   static inline int
>   grub_msdos_partition_is_empty (int type)
>   {
>     return (type == GRUB_PC_PARTITION_TYPE_NONE);
>   }
to allow booting from partitions of type 0 empty/none.
This should cause less confusion to the hundreds of young students atm 
wondering about "what the hell is formatting" ..

Best Regards,
#marcel