[e-acsl] fix assigns clauses for generated logic functions

src/plugins/e-acsl/Makefile.in

src/plugins/e-acsl/src/code_generator/logic_functions.ml

src/plugins/e-acsl/src/code_generator/smart_term.ml

src/plugins/e-acsl/src/code_generator/smart_term.mli

...lugins/e-acsl/tests/arith/oracle/functions_rec.res.oracle

src/plugins/e-acsl/tests/arith/oracle/gen_functions.c

src/plugins/e-acsl/tests/arith/oracle/gen_functions_rec.c

src/plugins/e-acsl/tests/bts/oracle/gen_issue-eacsl-177.c

src/plugins/e-acsl/tests/gmp-only/oracle/gen_functions.c