Fails due to:

abuild@marxinbox:~/rpmbuild/BUILD/grub-2.04/build-emu/grub-core> gcc
-DHAVE_CONFIG_H -I. -I../../grub-core -I..  -Wall -W  -DGRUB_MACHINE_EMU=1
-DGRUB_MACHINE=X86_64_EMU -I../../include -I../include
-DGRUB_FILE=\"disk/mdraid1x_linux.c\" -I. -I../../grub-core -I.. -I../..
-I../../include -I../include -I../../grub-core/lib/libgcrypt-grub/src/   
-D_FILE_OFFSET_BITS=64 -Os -Wall -W -Wshadow -Wpointer-arith -Wundef
-Wchar-subscripts -Wcomment -Wdeprecated-declarations -Wdisabled-optimization
-Wdiv-by-zero -Wfloat-equal -Wformat-extra-args -Wformat-security -Wformat-y2k
-Wimplicit -Wimplicit-function-declaration -Wimplicit-int -Wmain
-Wmissing-braces -Wmissing-format-attribute -Wmultichar -Wparentheses
-Wreturn-type -Wsequence-point -Wshadow -Wsign-compare -Wswitch -Wtrigraphs
-Wunknown-pragmas -Wunused -Wunused-function -Wunused-label -Wunused-parameter
-Wunused-value  -Wunused-variable -Wwrite-strings -Wnested-externs
-Wstrict-prototypes -g -Wredundant-decls -Wmissing-prototypes
-Wmissing-declarations  -Wextra -Wattributes -Wendif-labels -Winit-self
-Wint-to-pointer-cast -Winvalid-pch -Wmissing-field-initializers -Wnonnull
-Woverflow -Wvla -Wpointer-to-int-cast -Wstrict-aliasing -Wvariadic-macros
-Wvolatile-register-var -Wpointer-sign -Wmissing-include-dirs
-Wmissing-prototypes -Wmissing-declarations -Wformat=2 -freg-struct-return
-fno-dwarf2-cfi-asm -mno-stack-arg-probe -fno-asynchronous-unwind-tables
-fno-unwind-tables -mcmodel=large -fno-PIE -fno-pie -fno-stack-protector
-Wtrampolines -Werror   -ffreestanding  -fno-strict-aliasing
-fno-inline-functions-called-once  -MT disk/mdraid1x_module-mdraid1x_linux.o
-MD -MP -MF disk/.deps-core/mdraid1x_module-mdraid1x_linux.Tpo -c -o
disk/mdraid1x_module-mdraid1x_linux.o `test -f 'disk/mdraid1x_linux.c' || echo
'../../grub-core/'`disk/mdraid1x_linux.c
../../grub-core/disk/mdraid1x_linux.c: In function 'grub_mdraid_detect':
../../grub-core/disk/mdraid1x_linux.c:181:15: error: array subscript <unknown>
is outside array bounds of 'grub_uint16_t[0]' {aka 'short unsigned int[0]'}
[-Werror=array-bounds]
  181 |      (char *) &sb.dev_roles[grub_le_to_cpu32 (sb.dev_number)]
      |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../grub-core/disk/mdraid1x_linux.c:98:17: note: while referencing
'dev_roles'
   98 |   grub_uint16_t dev_roles[0]; /* Role in array, or 0xffff for a spare,
or 0xfffe for faulty.  */
      |                 ^~~~~~~~~
../../grub-core/disk/mdraid1x_linux.c:127:33: note: defined here 'sb'
  127 |       struct grub_raid_super_1x sb;
      |                                 ^~
cc1: all warnings being treated as errors

which is a GCC issue:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92326