autoconf to 2.70 breaks building gmake on apple silicon.

[CamilleScholtz]

With the error fork resource temporarily unavailable when executing missing, one of the files updated: 6f08110

Reverting to before this update fixes the error. I don't know if this only happens on macos, apple silicon, or what though.

[iamleot]

@Midar can you please give it a look? (over to committer)

[Midar]

Reproduced. This is indeed caused by the updated missing. I reverted missing and removed the comment in devel/autoconf/Makefile that says to update it, so that the next person updating autoconf does not break it again. Please verify this fixes it for you.

[Midar]

Closing as there has been no response, so I assume the fix for x86_64 also works on ARM. Please reopen if the issue persists.