Do not write a comma when varargs is the only argument

Fixes https://github.com/llvm/llvm-project/issues/56544

AsmWriter always writes ", ..." when a tail call has a varargs argument. This patch only writes the ", " when there is an argument before the varargs argument.

I did not write a dedicated test this for this change, but I modified an existing test that will test for a regression.

Reviewed By: avogelsgesang

Differential Revision: https://reviews.llvm.org/D137893



Signed-off-by: Adrian Vogelsgesang <avogelsgesang@salesforce.com>