[X86] Preserve BasePtr for LEA64_32r

When replacing FrameIndex with BasePtr, we must preserve BasePtr for
LEA64_32r since BasePtr is used later for stack adjustment if it is
the same as StackPtr.

Patch by H.J Lu <hjl.tools@gmail.com>

Differential Revision: https://reviews.llvm.org/D23575

llvm-svn: 283486