[clang-repl] value printing of calling functions with `void` return type ignores the call

Reproducer 1:
```c++
clang-repl> 1
(int) 1
clang-repl> extern "C" int printf(const char*, ...);
clang-repl> void foo() { printf("foo()\n"); }
clang-repl> foo();
foo()
clang-repl> foo()
clang-repl> foo();
foo()
```

The call to `foo()` without the semicolon, `;`, does not invoke the function.

Reproducer 2:
```c++
clang-repl> int x = 10;
clang-repl> x
(int) 10
clang-repl> void bar() { x = 100; }
clang-repl> bar()
clang-repl> x
(int) 10
clang-repl> bar();
clang-repl> x
(int) 100
```

Expected behaviour: The function should be invoked, or at least there should be an error saying invalid code.

cc @vgvassilev

Start by reproducing both examples in clang-repl and trace how a void-returning call entered without a semicolon is parsed and evaluated. Find the existing clang-repl handling for value printing and add regression coverage for both reproducers. Done means the call executes, or invalid input produces a clear error instead of being silently ignored.

Written by the indexing model from the issue text.