Nodes with no input would produced C code that can not compile

The bug was introduced in sha:bec478ee

https://www.cyber-neurones.org/2022/09/ubuntu-22-04-1-gcc-11-fcommon-issue-multiple-definition-of/

where the meant to be

The dependency on the clock was lost when the enum is translated into
an integer (because some expression were still refering to the enum type).

The fix was to index VarMap.t by string instead of Soc.var_expr in ActionsDeps.

In the -2c mode, in presence of extern types, I was defining them as int.
The idea was to have something that compiles, and then to ask the user
to redefine its extern types.

Now I define extern types as string (char*).

The rationale of this change is that before, the generated code was only
working for int, which is pretty useless as an extern type.

Have string by default is actually much more useful, for instance to use
string in a Lustre program.

Also, adapt to changes done in lutils, where the string type has ben added.
(sha:8619aa285ca8322ab9, i.e., > lutils  1.49.10)

Remove a lot of warnings (considered as errors by dune).

update the Arduino demo

The idea is to be able to take into account clock in node profiles
when generating the main simulation loop, and to avoid to read inputs
that are not present.

Indeed,
   x=y iff memcmp(x,y) == 0
not
   x=y iff memcmp(x,y) != 0
!

To do that, I have created a new dedicated module L2lExpandEnum, that
actually also deals with -eei (which was probably wrong, even if I
have not counter-exemple).

Use 1-hot encoding instead of log-encoding

I've fixed a bug in L2lExpandArrays that occurs on equation such as
  some_bool = (some_array1 = some_array2);

Also, I've rewritten Lv6Compile for more readability

Remove duplicated code when using SocMap.find and co

I've fixed that using memcmp, which should be fine since compared elements
are of the same types.

The previous change fixed program that contains type decl such as :
type t1;
type t2 = t1;

but not

type t1;
type t2 = t1^2 ;

or

type t2 = { xxx : t1^2 ; yyy : t1^2} ;

And now it works.

To fix it, I have include the _ext.h file into the lustre_type.h one.

The previous change fixed program that contains type decl such as :
type t1;
type t2 = t1;

but not

type t1;
type t2 = t1^2 ;

or

type t2 = { xxx : t1^2 ; yyy : t1^2} ;

And now it works.

To fix it, I have include the _ext.h file into the lustre_type.h one.