Add hasLoadFromStackSlot and hasStoreToStackSlot to return whether a
machine instruction loads or stores from/to a stack slot.  Unlike
isLoadFromStackSlot and isStoreFromStackSlot, the instruction may be
something other than a pure load/store (e.g. it may be an arithmetic
operation with a memory operand).  This helps AsmPrinter determine when
to print a spill/reload comment.

This is only a hint since we may not be able to figure this out in all
cases.  As such, it should not be relied upon for correctness.

Implement for X86.  Return false by default for other architectures.

llvm-svn: 87026