Synthesize x86 max/min instructions also for vectors (i.e. produce

maxps and maxpd).  This broke the sse41-blend.ll testcase by causing
maxpd to be produced rather than a cmp+blend pair, which is the reason
I tweaked it.  Gives a small speedup on doduc with dragonegg when the
GCC vectorizer is used.

llvm-svn: 139986