Fails to build with GNU as from binutils 2.35.1

```$ make all
cc -c -o start.o start.S
cc -g -fno-pie -Os -D__REAL_MODE__ -wrapper ./realify.sh -ffixed-r8 -ffixed-r9 -ffixed-r10 -ffixed-r11 -ffixed-r12 -ffixed-r13 -ffixed-r14 -ffixed-r15 -mno-red-zone -fcall-used-rbx -fno-jump-tables -fno-shrink-wrap -fno-schedule-insns2 -flive-range-shrinkage -fno-omit-frame-pointer -momit-leaf-frame-pointer -mpreferred-stack-boundary=3 -fno-delete-null-pointer-checks -c -o lisp.real.o lisp.c
/tmp/ccy4ZtIH.s: Assembler messages:
/tmp/ccy4ZtIH.s:189: Error: incorrect register `%dx' used with `l' suffix
/tmp/ccy4ZtIH.s:275: Error: incorrect register `%bx' used with `l' suffix
/tmp/ccy4ZtIH.s:355: Error: incorrect register `%bx' used with `l' suffix
/tmp/ccy4ZtIH.s:393: Error: incorrect register `%dx' used with `l' suffix
/tmp/ccy4ZtIH.s:979: Error: incorrect register `%ax' used with `l' suffix
/tmp/ccy4ZtIH.s:1080: Error: incorrect register `%ax' used with `l' suffix
make: *** [Makefile:60: lisp.real.o] Error 1
$ cc --version
cc (Ubuntu 10.2.0-13ubuntu1) 10.2.0
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ file (which cc)
/usr/bin/cc: symbolic link to /etc/alternatives/cc
$ file /etc/alternatives/cc
/etc/alternatives/cc: symbolic link to /usr/bin/gcc
```

What compiler & version are you using?

Start with Makefile line 60 and reproduce the failure using make all with GNU as from binutils 2.35.1. Then inspect lisp.c, start.S, and realify.sh alongside the reported assembler diagnostics. Done means the project builds successfully with that assembler version.

Written by the indexing model from the issue text.