cex: use usual routines for diagnostics about S/R conflicts
See previous commit. We go from
input.y: warning: 3 reduce/reduce conflicts [-Wconflicts-rr]
Shift/reduce conflict on token "⊕":
Example exp "+" exp • "⊕" exp
Shift derivation
exp
↳ exp "+" exp
↳ exp • "⊕" exp
to
input.y: warning: 3 reduce/reduce conflicts [-Wconflicts-rr]
input.y: warning: shift/reduce conflict on token "⊕" [-Wcounterexamples]
Example exp "+" exp • "⊕" exp
Shift derivation
exp
↳ exp "+" exp
↳ exp • "⊕" exp
with an hyperlink on -Wcounterexamples.
* src/counterexample.c (counterexample_report_shift_reduce):
Use complain.
* tests/counterexample.at, tests/diagnostics.at, tests/report.at:
Adjust.