Patch up configure tests for cpp to avoid problems when running gcc
4.5's cpp on makefiles. PR 45669.

Unfortunately, this does not by itself fix the build; now I'm getting

  ./temacs -batch -l loadup dump
  gmake[1]: *** [emacs] Segmentation fault

and I have a bad feeling that this may be the same issue that the
other emacs versions are sometimes hitting.

(dholland)