latest automake makes emacs bootstrap fail

[Jim Meyering]

Just a heads up:

In the very latest automake (from git), $MISSING is now invoked
with the --is-lightweight option.

That new usage causes emacs' bootstrap (also from git) to fail because
its missing script does not yet know about the --is-lightweight option.

In my case, I've simply copied automake's newer missing script
into my cloned emacs build tree, and with that the emacs bootstrap
now succeeds.

Jim