In TargetLowering::LowerCallTo, don't assert that

In TargetLowering::LowerCallTo, don't assert that
the return value is zero-extended if it isn't
sign-extended.  It may also be any-extended.
Also, if a floating point value was returned
in a larger floating point type, pass 1 as the
second operand to FP_ROUND, which tells it
that all the precision is in the original type.
I think this is right but I could be wrong.
Finally, when doing libcalls, set isZExt on
a parameter if it is "unsigned".  Currently
isSExt is set when signed, and nothing is
set otherwise.  This should be right for all
calls to standard library routines.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47122 91177308-0d34-0410-b5e6-96231b3b80d8