[llvm] Implement reserveAllocationSpace for SectionMemoryManager (PR #71968)

[Lang Hames via llvm-commits]

lhames wrote:

@gmarkall's comment sounds promising:
> I've received various reports that this fixes issues related to https://github.com/llvm/llvm-project/issues/71963 on both macOS and LinuxAArch64 systems, and no reports of adverse effects - so FWIW, my confidence in this patch being a good fix is quite high.

On that basis I'm ok with this landing in main. However, if we see any issues related to it the bias should be to revert, rather than try to fix issues (if the fixes would introduce further changes in behavior): We're discussing deprecation and removal of MCJIT and RuntimeDyld (see https://discourse.llvm.org/t/rfc-add-deprecation-warnings-to-mcjit-and-runtimedyld/80465 and https://discourse.llvm.org/t/rfc-removing-mcjit-and-runtimedyld/80464) and the goal at this point is stability rather than bug-fixes.

If any of you are using MCJIT directly you'll want to look at switching to ORC / LLJIT. If you're already on ORC / LLJIT please be aware that we'll be switching to `JITLink` by default for jit-linking. JITLink's default memory manager already addresses the out-of-range issues, so hopefully they just won't come up after the switch.

https://github.com/llvm/llvm-project/pull/71968