[llvm] [llvm] simplify and clean-up DemangleConfig.h (PR #149163)

[Jordan Rupprecht via llvm-commits]

rupprecht wrote:

> It should be safe for the Demangle component library to depend on Support, so there is no need for it to maintain copies of macros defined in llvm/Support/Compiler.h.

This commit creates a library layering violation because Support already depends on Demangle, e.g. https://github.com/llvm/llvm-project/blob/324773e238026c5d4f501213678a89bf411e1509/llvm/lib/Support/Unix/Signals.inc#L38

Is there another way you can land this commit w/o creating a cycle?

https://github.com/llvm/llvm-project/pull/149163