[GlobalISel][CallLowering] Rename isArgumentHandler() -> isIncomingArgumentHandler()

Previous name and comment incorrectly implied it was just for formal arg handlers,
which is not true.

llvm-svn: 367945
diff --git a/llvm/lib/Target/ARM/ARMCallLowering.cpp b/llvm/lib/Target/ARM/ARMCallLowering.cpp
index 00f21a9..a507756 100644
--- a/llvm/lib/Target/ARM/ARMCallLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMCallLowering.cpp
@@ -286,7 +286,7 @@
                        CCAssignFn AssignFn)
       : ValueHandler(MIRBuilder, MRI, AssignFn) {}
 
-  bool isArgumentHandler() const override { return true; }
+  bool isIncomingArgumentHandler() const override { return true; }
 
   Register getStackAddress(uint64_t Size, int64_t Offset,
                            MachinePointerInfo &MPO) override {