[clang] [clang-repl][CodeGen] Add setOptLevel, #pragma clang repl optimize(N) (PR #214793)

[Vassil Vassilev via cfe-commits]

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@@ -216,6 +221,80 @@ static llvm::Error ExecuteIncrementalAction(CompilerInstance &CI,
   return llvm::Error::success();
 }
 
+// '#pragma clang repl optimize(<opt>)' sets the optimization level and size
+// used to emit modules for input parsed after the pragma. <opt> is an -O flag
+// spelled without the leading dash, e.g. O2 or Os.
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vgvassilev wrote:

```suggestion
// spelled without the leading dash, e.g. O0, O1,...
```
please enumerate what's currently supported.

https://github.com/llvm/llvm-project/pull/214793