C++: Fix duplicate result types

In a couple of cases, we use `glval<unknown>` as the result type of an instruction because we can't come up with anything better. Two examples are the result of `VariableAddress[#ellipsis]`, and the address of the temp variable that holds the lvalue result of the conditional operator in `(a ? b : c) = y`. In both cases, we call `getTypeForGLValue(any(UnknownType t))`, but that would have multiple results because `result.hasType(any(UnknownType t), true)` also holds for `CppFunctionGLValueType`. I tightened the result type to ensure we get the right one.

Author: Dave Bartolomeo

cpp/ql/src/semmle/code/cpp/ir/internal/CppType.qll

@@ -362,7 +362,7 @@ CppType getTypeForPRValueOrUnknown(Type type) {
 /**
  * Gets the `CppType` that represents a glvalue of type `type`.
  */
-CppType getTypeForGLValue(Type type) { result.hasType(type, true) }
+CppGLValueAddressType getTypeForGLValue(Type type) { result.hasType(type, true) }
 
 /**
  * Gets the `CppType` that represents a prvalue of type `int`.