[Eva] Cvalue domain: uses the valuation only for lvalues of scalar type.

The cvalues cannot precisely represent structs and arrays: they are irrelevant
and could degrade the state precision for such lvalues.

src/plugins/value/domains/cvalue/cvalue_transfer.ml

@@ -60,7 +60,7 @@ let update valuation t =
   let process exp record t =
     match exp.enode with
     | Lval lv ->
-      if record.reductness = Reduced
+      if record.reductness = Reduced && Cil.isScalarType (Cil.typeOfLval lv)
       then
         let {v; initialized; escaping} = record.value in
         let v = unbottomize v in

tests/value/oracle_multidim/struct2.res.oracle

 53a54,55
 > [kernel] struct2.i:78: Warning: 
 >   all target addresses were invalid. This path is assumed to be dead.
-75a78,81
-> [eva] struct2.i:173: 
->   Assigning imprecise value to ((s1.c)->c)->b
->   (pointing to s2 with offsets {352}).
->   The imprecision originates from Misaligned Bottom
-129,130c135
-<   s8.a ∈ {0}
-<     .b ∈ {{ &a }}
----
->   s8 ∈ {{ garbled mix of &{a} (origin: Misaligned Bottom) }}
-136,137d140
+136,137d137
 <   tab4[0] ∈ {0; 2}
 <       [1] ∈ {0}
-206c209
+206c206
 <     s4.e[0].a; s8.b; s7; tab1[0..1]; tab2[0..1]; tab3[0..1]; tab4[0]; tab5[0];
 ---
 >     s4.e[0].a; s8.b; s7; tab1[0..1]; tab2[0..1]; tab3[0..1]; tab5[0];