Fixed some spiller bugs exposed by the recent two-address code changes. Now

Fixed some spiller bugs exposed by the recent two-address code changes. Now
there may be other def(s) apart from the use&def two-address operand. We need
to check if the register reuse for a use&def operand may conflicts with another
def. Provide a mean to recover from the conflict if it is detected when the
defs are processed later.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31439 91177308-0d34-0410-b5e6-96231b3b80d8