yacc: remove trailing end of line at end of file

There are still spurious spaces at the end of some lines.  But this is
addressed in the master branch, and I am reluctant to try to backport
this.

* data/yacc.c, data/glr.c, data/lalr1.cc, data/glr.cc: here.
* tests/calc.at (AT_CHECK_SPACES): New.
Use it.
Be sure not to introduce trailing empty lines in the *.y files.
* NEWS: Doc it.
* cfg.mk (syntax-check): Remove the exception.