glr.cc: %defines is no longer mandatory

* data/glr.cc: No longer require %defines.
When it is not given, define the position and location classes instead
of including their headers.
(b4_shared_declarations): Use the original parse-params.
* data/glr.c (b4_shared_declarations): Define only if undefined.
* tests/actions.at, tests/calc.at: No longer force the use of %defines
for glr.cc.
* NEWS: Doc it.

tests/actions.at

@@ -1278,7 +1278,6 @@ AT_BISON_OPTION_PUSHDEFS([%skeleton "$1"])
 
 AT_DATA_GRAMMAR([[input.y]],
 [[%skeleton "$1"
-%defines   // FIXME: Mandated by glr.cc.
 %debug
 %code requires
 {