The `__eacsl_globals_clean()` global function is only created if there
are globals variables. A `return;` statement is added at the end of the
function to satisfy Frama-C invariants.

The `e-acsl-gcc.sh` only looked for the Frama-C executable in the
`$PATH`. This commit updates the search for Frama-C to be able
to detect the binary if installed in a folder not added to the path,
or if running the script from the development sources.

The contracts are updated to mention the behaviors in the contracts of
`stdlib.h` and satisfy Eva.

[eacsl] Merge the specifications from the RTL functions with the corresponding functions from the user's project

The Variadic plugin translation is incompatible with the use of option
 `-e-acsl-validate-format-strings`, so add the option
 `-variadic-no-translation` if the user activated the validation of
 format strings.

The `-P` option does not exist.

The `-p` option does not exist.

- Add prefix parameter to `Smart_stmt.rtl_call`
- Remove `Smart_stmt.lib_call` and replace it with calls to `Smart_stmt.rtl_call`
- Add `Smart_stmt.call` to call an arbitrary function from the AST
- Use `Smart_stmt.call` when generating calls to `malloc` and `free