Eliminate the explicit volatile fields in LoadInst and StoreInst. This shrinks

Eliminate the explicit volatile fields in LoadInst and StoreInst.  This shrinks
LoadInst from 60 -> 56 bytes and StoreInst from 76 -> 72 bytes.

Note however, that this doesn't actually save any memory on common systems
where 'malloc' returns 8-byte aligned memory, as the saved space is replaced
by useless alignment padding.  :(

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@20046 91177308-0d34-0410-b5e6-96231b3b80d8