Simplify code for returning a struct for Darwin x86-32 ABI. Use a better type...

Simplify code for returning a struct for Darwin x86-32 ABI.  Use a better type for a function returning a struct containing only a pointer.  Handle the edge case of a struct containing only a float or double plus some dead padding instead of asserting.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@144960 91177308-0d34-0410-b5e6-96231b3b80d8