[clang-repl][Orc] Export executable symbols in ClangReplInterpreterExceptionTests

In Orc runtime, we use `dlopen(nullptr, ...)` to open current executable and use `dlsym` to find addresses of symbols, this requires `-rdynamic` flag.

As `llvm/CMakeLists.txt` suggests

```
# Make sure we don't get -rdynamic in every binary. For those that need it,
# use export_executable_symbols(target).
```
This patch exports symbols in `ClangReplInterpreterExceptionTests`. This also fixes `ClangReplInterpreterExceptionTests` is skipped on ppc64 when jitlink is used.

Reviewed By: v.g.vassilev

Differential Revision: https://reviews.llvm.org/D159167