Model sqrtss as a binary operation with one source operand tied to the destination (PR14221)

This is a continuation of r167064 ( http://llvm.org/viewvc/llvm-project?view=revision&revision=167064 ).
That patch started to fix PR14221 ( http://llvm.org/bugs/show_bug.cgi?id=14221 ), but it was not completed. 

Differential Revision: http://reviews.llvm.org/D6330

llvm-svn: 224624