Prevent obscure and incorrect tail-call optimization.

In this instance we are generating the tail-call during legalizeDAG.  The 2nd
floor call can't be a tail call because it clobbers %xmm1, which is defined by
the first floor call.  The first floor call can't be a tail-call because it's
not in the tail position.  The only reasonable way I could think to fix this
in a target-independent manner was to check for glue logic on the copy reg.

rdar://10930395

llvm-svn: 151877