"Eager macro-expansion failure: (excessive-variable-binding)"

[Lars Ingebrigtsen]

Doing a bootstrap today I get:

  ELC      ../lisp/abbrev.elc
Local variable error: (error "Eager macro-expansion failure: 
(excessive-variable-binding)")
  ELC      ../lisp/bindings.elc
Local variable error: (error "Eager macro-expansion failure: 
(excessive-variable-binding)")
  ELC      ../lisp/buff-menu.elc
Local variable error: (error "Eager macro-expansion failure: 
(excessive-variable-binding)")
  ELC      ../lisp/button.elc
Local variable error: (error "Eager macro-expansion failure: 
(excessive-variable-binding)")
(etc etc)

I haven't tried debugging this -- perhaps it's obvious to somebody
what's triggering this?  And would it perhaps be possible to improve
this error message to make it give a hint about where it's finding the
problem?