[Eva] Fixes a bug on goto statement skipping local variable declarations.

See merge request frama-c/frama-c!4245

Easier use of make_machdep.py in installed Frama-C

See merge request frama-c/frama-c!4215

"[headers] temporary fix"

See merge request frama-c/frama-c!4246

[e-acsl] rename misleading variable

See merge request frama-c/frama-c!4240

All variables local to a block are now introduced in domain states as soon as
the analysis enters the block. This ensures all variables in scope have always
been introduced in domain states, even when a goto statement jumps to a block
after the declaration of some local variables, skipping their initializations
(these variables would have been introduced in the states, but not initialized).

As a downside, variables explicitly initialized at declaration enter the scope
too early, as they should be introduced on the fly when encountering their
[Local_init] instruction.

Better callstacks in Eva

See merge request frama-c/frama-c!4207

Replaces [set_call_stack] by [init_call_stack].
Removes [legacy_call_stack], which is never used.

Comments all function in the interface.

- The callstack type is not private anymore. Only the current callstack in
  Eva_utils should not be modified without using push/pop; everywhere else,
  functions can freely create callstacks if needed.
  Removes function [change_thread], as it is now useless.

- [pop] only returns the new callstack: this simplifies all its current uses.

- new function [last_caller] returning the function from the penultimate call.

- new function [pretty_debug] to allow using Hptmap on callstacks.

In Eva_utils, the reference to the current callstack is None until the
analysis of the main function starts.

[register_initial_state] now takes the kernel_function as argument.
This avoids using [Callstacks.top_kf] in the store.