[X86][SSE] Float comparisons can sometimes be safely commuted

For ordered, unordered, equal and not-equal tests, packed float and double comparison instructions can be safely commuted without affecting the results. This patch checks the comparison mode of the (v)cmpps + (v)cmppd instructions and commutes the result if it can.

Differential Revision: http://reviews.llvm.org/D7178

llvm-svn: 227145