[E-ACSL] fixed bug #1398 about calling variadic functions

src/plugins/e-acsl/TODO

src/plugins/e-acsl/pre_visit.ml

src/plugins/e-acsl/tests/e-acsl-runtime/bts1398.c

...s/e-acsl/tests/e-acsl-runtime/oracle/bts1398.1.err.oracle

...s/e-acsl/tests/e-acsl-runtime/oracle/bts1398.1.res.oracle

...ins/e-acsl/tests/e-acsl-runtime/oracle/bts1398.err.oracle

...ins/e-acsl/tests/e-acsl-runtime/oracle/bts1398.res.oracle

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_bts1398.c

...plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_bts13982.c