Use gdisk instead of fdisk when printing partition table

Makefile

@@ -287,7 +287,12 @@ build/os.file: ${os_filename} build/check_makefile
 	file -kr $< > $@
 
 build/os.fdisk: ${os_filename} build/check_makefile
-	fdisk -l $< > $@
+#       gdisk commands:
+#         * Print partition table
+#         * Recovery and transformation options
+#         * print prOtective MBR table
+#         * Quit
+	printf 'p\nr\no\nq\n' | gdisk $< > $@
 
 build/os.offsets: ${offset_names:%=build/offsets/%.hex} build/check_makefile
 	grep '^' ${offset_names:%=build/offsets/%.hex} | sed -e 's/:/: 0x/' > $@