Add GPT partition support

People creating the media through File System Transposition [1] rather than DD
copy may end up with a media that uses a GPT partition table rather than MBR.

So add GPT support to GRUB, as a low cost beneficial change.

For reference, File System Transposition is the default method used by Rufus
and other utilities for creating bootable media from an ISO, and it allows
users to select GPT instead over MBR, in which case memtest86+ will not boot.

[1] https://lists.gnu.org/archive/html/grub-devel/2022-06/msg00024.html

build32/Makefile

@@ -228,7 +228,7 @@ GRUB_LIB_DIR ?= /usr/lib/grub
 
 GRUB_MKIMAGE := $(shell command -v grub2-mkimage || command -v grub-mkimage)
 
-GRUB_MODULES = iso9660 fat part_msdos all_video font gfxterm gfxmenu \
+GRUB_MODULES = iso9660 fat part_msdos part_gpt all_video font gfxterm gfxmenu \
                boot chain configfile echo ls
 
 grub-eltorito.img:

build64/Makefile

@@ -227,7 +227,7 @@ GRUB_LIB_DIR ?= /usr/lib/grub
 
 GRUB_MKIMAGE := $(shell command -v grub2-mkimage || command -v grub-mkimage)
 
-GRUB_MODULES = iso9660 fat part_msdos all_video font gfxterm gfxmenu \
+GRUB_MODULES = iso9660 fat part_msdos part_gpt all_video font gfxterm gfxmenu \
                boot chain configfile echo ls
 
 grub-eltorito.img: