Added new X86 patterns to select SSE scalar fp arithmetic instructions from

a vector packed single/double fp operation followed by a vector insert.

The effect is that the backend coverts the packed fp instruction
followed by a vectro insert into a SSE or AVX scalar fp instruction.

For example, given the following code:
   __m128 foo(__m128 A, __m128 B) {
     __m128 C = A + B;
     return (__m128) {c[0], a[1], a[2], a[3]};
   }

 previously we generated:
   addps %xmm0, %xmm1
   movss %xmm1, %xmm0
 
 we now generate:
   addss %xmm1, %xmm0

llvm-svn: 197145