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

[Ben Howe via llvm-commits]

bmhowe23 wrote:

Hi - is this PR still in work? The changes in this PR helped to resolve a [bug](https://github.com/NVIDIA/cuda-quantum/issues/1421) that we saw in CUDA-Q when using ARM, so I was curious if this had a path forward for getting merged into `main`. (However, we did have to change the default value of `ReserveAlloc` from `false` to `true` in order for it to fix our problem.)

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