[clang] [clang-repl] Enable native CPU detection by default (PR #77491)

[Stefan Gränitz via cfe-commits]

weliveindetail wrote:

Oh and this matches the default behavior in Orc host detection btw: https://github.com/llvm/llvm-project/blob/release/17.x/llvm/lib/ExecutionEngine/Orc/JITTargetMachineBuilder.cpp#L35

https://github.com/llvm/llvm-project/pull/77491