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

[Aaron Jomy via cfe-commits]

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@@ -22,6 +22,8 @@
 #include "clang/Sema/Lookup.h"
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aaronj0 wrote:

@vgvassilev I've added some lit level tests, now that #218735 has landed and the IR can be checked.

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