The SSE version differences for fmin/fmax are more involved than I thought.

- x87: no min or max.
- SSE1: min/max for single precision scalars and vectors.
- SSE2: min/max for single and double precision scalars and vectors.
- AVX: as SSE2, but also supports the wider ymm vectors. (this is covered by the isTypeLegal check)

llvm-svn: 140296