Doubts related to dlopen and dlclose

Hey @sbc100,

I think you might be able to help me out here.

So clang-repl can do the undo operation to surpass redefinitions and stuff. For eg
```
clang-repl> int y = 50;
clang-repl> const char* y = "Hello World";
In file included from <<< inputs >>>:1:
input_line_6:1:13: error: redefinition of 'y' with a different type: 'const char *' vs 'int'
1 | const char* y = "Hello World";
| ^
input_line_5:1:5: note: previous definition is here
1 | int y = 50;
| ^
error: Parsing failed.

clang-repl> extern "C" int printf(const char*, ...);
clang-repl> int x = 50;
clang-repl> %undo
clang-repl> const char* x = "Hello World";
clang-repl> auto r = printf("%s\n", x);
Hello World
```

Now I was trying to extend the same functionality while we're running clang-repl in the browser.

So basically
1) for executing we use AddModule : I think I might have explained the approach here in the past. We use `dlopen` for this. Each cell/code block gives us a side module which should be loaded up top of the main module using dlopen

`code -> PTU -> LLVM IR -> wasm object -> wasm binary -> loaded on top of main module using dlopen`

This is done here https://github.com/llvm/llvm-project/blob/main/clang/lib/Interpreter/Wasm.cpp#L120-L126

2) for [undo](https://github.com/llvm/llvm-project/blob/44b9f5eeab63dbf7d4e4ebc87dfedca5c42708b6/clang/lib/Interpreter/Interpreter.cpp#L695) we use [removeModule](https://github.com/llvm/llvm-project/blob/44b9f5eeab63dbf7d4e4ebc87dfedca5c42708b6/clang/lib/Interpreter/Wasm.cpp#L131) : My approach here was as we load the module, we just need to keep track of the handle and unload it. I thought we can put `dlclose` to use for the same.

**So as of now as removeModule was not implemented**, but I thought of introducing this small diff for implementation

https://github.com/llvm/llvm-project/blob/main/clang/lib/Interpreter/Wasm.cpp#L120-L126 (Has few debug logs too)

i) So I just keep track of the modules
ii) locate the handle to the unloaded.
iii) Unload using dlclose