[clang] [llvm] Support alternative sections for patchable function entries (PR #131230)

[Sami Tolvanen via llvm-commits]

samitolvanen wrote:

@MaskRay here's a draft implementation of the patchable function entry extension [discussed in LKML](https://lore.kernel.org/lkml/Y1QEzk%2FA41PKLEPe@hirez.programming.kicks-ass.net/) a couple of years ago. Could you please take a look and see if this seems reasonable?

https://github.com/llvm/llvm-project/pull/131230