Fix a pretty serious misfeature of the inliner: if it inlines a function

with multiple return values it inserts a PHI to merge them all together.
However, if the return values are all the same, it ends up with a pointless
PHI and this pointless PHI happens to really block SRoA from happening in 
at least a silly C++ example written by Doug, but probably others.  This 
fixes rdar://7339069.

llvm-svn: 85206