C++: Fix FP on unevaluated code

This fixes false positives on tenzir/vast.

Author: jbj

cpp/ql/src/Likely Bugs/Likely Typos/CompareWhereAssignMeant.ql

@@ -15,7 +15,10 @@ import cpp
 
 from ExprInVoidContext op
 where
-  op instanceof EQExpr
-  or
-  op.(FunctionCall).getTarget().hasName("operator==")
+  not op.isUnevaluated() and
+  (
+    op instanceof EQExpr
+    or
+    op.(FunctionCall).getTarget().hasName("operator==")
+  )
 select op, "This '==' operator has no effect. The assignment ('=') operator was probably intended."

cpp/ql/test/query-tests/Likely Bugs/Likely Typos/CompareWhereAssignMeant/CompareWhereAssignMeant.expected

@@ -6,4 +6,3 @@
 | test.cpp:39:23:39:28 | ... == ... | This '==' operator has no effect. The assignment ('=') operator was probably intended. |
 | test.cpp:42:23:42:28 | ... == ... | This '==' operator has no effect. The assignment ('=') operator was probably intended. |
 | test.cpp:51:13:51:13 | call to operator== | This '==' operator has no effect. The assignment ('=') operator was probably intended. |
-| test.cpp:61:44:61:51 | ... == ... | This '==' operator has no effect. The assignment ('=') operator was probably intended. |

cpp/ql/test/query-tests/Likely Bugs/Likely Typos/CompareWhereAssignMeant/test.cpp

@@ -58,6 +58,6 @@ void f(void) {
 // This pattern is used to emulate C++20 concepts in a way that's very light on
 // template syntax.
 template<typename T1, typename T2>
-auto sfinaeTrick(T1 x1, T2 x2) -> decltype(x1 == x2, bool()) { // GOOD [FALSE POSITIVE]
+auto sfinaeTrick(T1 x1, T2 x2) -> decltype(x1 == x2, bool()) { // GOOD
   return x1 == x2;
 }