[aarch64] grub-efi cannot be built because of qemu changes

[Ricardo Wurmus]

Hi Guix,

commit 71b8707100e2fbc00f123566717ba3958c6afabb seems to have broken
reconfiguration of my aarch64 machine.

That commit adds openbios-qemu-ppc to qemu, but the build of
openbios-qemu-ppc fails on aarch64:

--8<---------------cut here---------------start------------->8---
starting phase `configure'
Configuring OpenBIOS on aarch64 for qemu-ppc
Initializing build tree 
/tmp/guix-build-openbios-qemu-ppc-1.1.drv-0/source/obj-ppc...ok.
Creating target config.mak...ok.
Creating target rules.mak...ok.
Creating config files...ok.
phase `configure' succeeded after 0.9 seconds
starting phase `patch-generated-file-shebangs'
phase `patch-generated-file-shebangs' succeeded after 0.0 seconds
starting phase `build'
Building OpenBIOS for ppc
Building...
error:
/gnu/store/gm5mbaxkqhzafwy0wnimrg53j884glxn-linux-libre-headers-5.10.35/include/asm/sigcontext.h:128:2:
 error: unknown type name ‘__u32’
  128 |  __u32 size; /* size in bytes of the extra space */
      |  ^~~~~
/gnu/store/gm5mbaxkqhzafwy0wnimrg53j884glxn-linux-libre-headers-5.10.35/include/asm/sigcontext.h:129:2:
 error: unknown type name ‘__u32’
  129 |  __u32 __reserved[3];
      |  ^~~~~
/gnu/store/gm5mbaxkqhzafwy0wnimrg53j884glxn-linux-libre-headers-5.10.35/include/asm/sigcontext.h:136:2:
 error: unknown type name ‘__u16’
  136 |  __u16 vl;
      |  ^~~~~
/gnu/store/gm5mbaxkqhzafwy0wnimrg53j884glxn-linux-libre-headers-5.10.35/include/asm/sigcontext.h:137:2:
 error: unknown type name ‘__u16’
  137 |  __u16 __reserved[3];
      |  ^~~~~
make[1]: *** [rules.mak:83: host/kernel/bootstrap.o] Error 1
make[1]: *** Waiting for unfinished jobs....
make[1]: Leaving directory 
'/tmp/guix-build-openbios-qemu-ppc-1.1.drv-0/source/obj-ppc'
make: *** [Makefile:19: build] Error 1
error: in phase 'build': uncaught exception:
%exception #<&invoke-error program: "make" arguments: ("-j" "2") exit-status: 2 
term-signal: #f stop-signal: #f> 
phase `build' failed after 0.6 seconds
--8<---------------cut here---------------end--------------->8---

What can be done about this?

With openbios-qemu-ppc failing, qemu-minimal cannot be built, so
grub-efi cannot be built on aarch64.

-- 
Ricardo