Allow casts from any type to void

[michael-schwarz]

Any expression may be cast to void according to the standard if an expression is only evaluated for its side-effects. We currently limit this to (TInt _ | TEnum _ | TPtr _ ) for some reason.

Closes #91

[michael-schwarz]

The build failures for old versions of OCaml are strange and probably unrelated as they cause all tests to fail not just the new ones.

Maybe due to old dune versions and some after effect of #104 @sim642?

Output for failing OCaml <4.07.1

File "test/dune", line 1, characters 0-180:
1 | (rule
2 |  (alias runtest)
3 |  (deps (alias_rec ../cilly) (package goblint-cil) (source_tree .))
4 |  (action (setenv "CC" "\"%{read-lines:../bin/real-gcc}\"" (run ./testcil -r --regrtest))))
(cd _build/default/test && ./testcil -r --regrtest)
Test infrastructure for CIL on linux
There are 431 tests enabled

Output for working OCaml

(cd _build/default/test && ./testcil -r --regrtest)
Test infrastructure for CIL on linux
There are 431 tests enabled

[michael-schwarz]

These tests indeed already seem to fail on develop now.

[sim642]

That's odd, because they all passed at the time and the first attempt (from two days ago) on develop also passed. Maybe something on opam of our dependencies regressed since then?

[sim642]

Looks like a problem with the seq package update: c-cube/seq#14. We can just ignore those failures for the moment.