X86 address mode isel tweak. If the base of the address is also used by a CopyToReg (i.e. it's likely live-out), do not fold the sub-expressions into the addressing mode to avoid computing the address twice. The CopyToReg use will be isel'ed to a LEA, re-use it for address instead.

This is not yet enabled.

llvm-svn: 68082