[BUG] Infinite make recursion when configure.ac changes

From a pristine master checkout:

  $ make configure && ./configure make
  ... # All successfull
  $ touch configure.ac
  $ make
    GEN config.status
  make[1]: Entering directory `/storage/home/stefano/git/src'
    GEN config.status
  make[2]: Entering directory `/storage/home/stefano/git/src'
    GEN config.status
  make[3]: Entering directory `/storage/home/stefano/git/src'
    GEN config.status
  make[4]: Entering directory `/storage/home/stefano/git/src'
    GEN config.status
  make[5]: Entering directory `/storage/home/stefano/git/src'
    GEN config.status
  ...

and I have to hit ^C to interrupt that recursion.

This seems due to the change in commit v1.7.12.4-1-g1226504: the
issue is still present there, but no longer is in the preceding
commit 7e201053 (a.k.a. v1.7.12.4).

I haven't investigated this any further for the moment.

Regards,
  Stefano