Loosen up an assertion to allow intrinsics. I really have no

idea what this code (findNonImmUse) does, so I'm only guessing 
that this is the right thing.  It would be really really nice
if this had comments and perhaps switched to SmallPtrSet
(hint hint) :)

This fixes rdar://5886601, a crash on gcc.target/i386/sse4_1-pblendw.c

llvm-svn: 50252