yacc.c, glr.c: a better YY_LOCATION_PRINT

* data/c.m4 (b4_yy_location_print_define): New.
Now issues "short" locations, e.g., "1.1" instead of "1.1-1.1".
Was initially a function, but then we face "static but unused"
warnings.
Simpler as a macro.
* tests/local.at, data/glr.c, data/yacc.c: Use it instead of duplicating.
* tests/actions.at: Adjust expectations.