This patch is the first step towards ensuring MergeConsecutiveStores correctly handles non-temporal stores:
1 - When merging load\stores we must ensure that they all have the same non-temporal flag. This is unlikely to occur, but can in strange cases where we're storing at the end of one page and the beginning of another.
2 - The merged load\store node must retain the non-temporal flag.
After this I need to improve alignment handling - in most cases we shouldn't merge nt-ops unless they are naturally aligned - either we just prevent it in all cases or we refactor canMergeStoresTo\allowsMemoryAccess to include access to the alignment and MMO flags as well?