[RISCV][GISel] Pass the IsFixed flag into CC_RISCV for outgoing arguments.

This is needed to make FP values be pased in a GPR as required by
the variadic function ABI.

Author: topperc

llvm/lib/Target/RISCV/GISel/RISCVCallLowering.cpp

@@ -48,7 +48,7 @@ struct RISCVOutgoingValueAssigner : public CallLowering::OutgoingValueAssigner {
     const RISCVSubtarget &Subtarget = MF.getSubtarget<RISCVSubtarget>();
 
     return RISCVAssignFn(DL, Subtarget.getTargetABI(), ValNo, ValVT, LocVT,
-                         LocInfo, Flags, State, /*IsFixed=*/true, IsRet,
+                         LocInfo, Flags, State, Info.IsFixed, IsRet,
                          Info.Ty, *Subtarget.getTargetLowering(),
                          /*FirstMaskArgument=*/std::nullopt);
   }