[SparcV9]: Implement lowering of long double (fp128) arguments in Sparc64 ABI.
Also, pass fp128 arguments to varargs through integer registers if necessary.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198145 91177308-0d34-0410-b5e6-96231b3b80d8