gcc-ar: Remove code duplication.

gcc-ar: Remove code duplication.

From c3f3b2fd53291805b5d0be19df6d1a348c5889ec Mon Sep 17 00:00:00 2001
From: Costas Argyris <costas.argyris@gmail.com>
Date: Thu, 15 Jun 2023 12:37:35 +0100
Subject: [PATCH] gcc-ar: Remove code duplication.

Preparatory refactoring that simplifies by eliminating
some duplicated code, before trying to fix 77576.
I believe this stands on its own regardless of the PR.
It also saves a nargv element when we have a plugin and
three when not.

gcc/
	* gcc-ar.cc (main): Refactor to slightly reduce code
	duplication.  Avoid unnecessary elements in nargv.