The message for conflicting mcpu and march previously printed the
architecture of the CPU instead of the CPU name, as well as omitting the
extensions to the march string. This patch corrects both errors. This
patch fixes PR target/87612.

2020-02-27  Joel Hutton  <Joel.Hutton@arm.com>

        PR target/87612
        * config/aarch64/aarch64.c (aarch64_override_options): Fix
        misleading warning string.