[llvm] [MC] Allocate MCFragment with a bump allocator (PR #96402)

[Alexis Engelke via llvm-commits]

aengelke wrote:

I'm admittedly quite surprised about the max-rss increase -- that shouldn't happen (at least not to such an extent), because fragments are still freed when sections are freed, which is done by MCContext::reset(), which will free the allocated memory for fragments. Sections are freed before fragments (at least, if DoAutoReset is set, which it looks like it is? If it's not, that might be problematic...), so fragment destructors should get called and free associated contents/fixups. I guess we are overlooking something. Will see if I find time to look at this tomorrow.

https://github.com/llvm/llvm-project/pull/96402