[e-acsl] shorter name for generated variable

src/plugins/e-acsl/TODO

...ugins/e-acsl/tests/e-acsl-runtime/oracle/arith.res.oracle

.../e-acsl/tests/e-acsl-runtime/oracle/comparison.res.oracle

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_arith.c

...ugins/e-acsl/tests/e-acsl-runtime/oracle/gen_comparison.c

...e-acsl/tests/e-acsl-runtime/oracle/gen_integer_constant.c

...l/tests/e-acsl-runtime/oracle/integer_constant.res.oracle

src/plugins/e-acsl/visit.ml