[llvm] [cmake] Optimize RelWithDebInfo compiler options on windows (PR #101533)

[Tom Stellard via llvm-commits]

tstellar wrote:

I think the rule of thumb is not to modify the builtin CMAKE_* variables.  It's hard to predict how this may impact a user who wants to set their own custom flags.  See https://alexreinking.com/blog/how-to-use-cmake-without-the-agonizing-pain-part-2.html

https://github.com/llvm/llvm-project/pull/101533