[Buildroot] Build error when building two GRUB2 configurations (race condition)

[Stefan Agner]

Hello,

In Home Assistant OS we use the capability to build two GRUB2 binaries
by enabling these two configurations:

BR2_TARGET_GRUB2_I386_EFI=y  
BR2_TARGET_GRUB2_X86_64_EFI=y

Every now and then a from scratch build seems to fail with the following
error:

config.status: creating config-util.h
In file included from ../include/grub/disk.h:***,
                 from ../include/grub/file.h:26,
                 from ../grub-core/kern/emu/hostfs.c:23:
./config.h:38:10: fatal error: ./config-util.h: No such file or
directory
   38 | #include <config-util.h>
      |          ^~~~~~~~~~~~~~~
compilation terminated.

At least in this instance it seems to be the second configuration
x86_64-efi which fails (as the previous >>> grub2 2.04 Building i386-efi
succeeds).

The full build log can be found here:
https://pipelines.actions.githubusercontent.com/serviceHosts/dff1d65b-5367-4f4f-a0ee-c2bf0f874fbd/_apis/pipelines/1/runs/8778/signedlogcontent/14?urlExpires=2022-06-25T16%3A32%3A02.7601449Z&urlSigningMethod=HMACV1&urlSignature=c9ayjKpOOIoTexbMMXYB8A1G6UwmGfhBwTdtxTE3wmI%3D

I haven't dig into it really, maybe someone with some familiarity of the
GRUB2 (multi-platform) build system has some idea?

Best regards,
Stefan