As of recently the -march,-mcpu,-mtune strings in the error messages are
now quoted.
This patch adjusts the testcases in gcc.target/aarch64/ that had started
failing due to that change.

	PR target/89719
	* gcc.target/aarch64/spellcheck_4.c: Adjust dg-error string.
	* gcc.target/aarch64/spellcheck_5.c: Likewise.
	* gcc.target/aarch64/spellcheck_6.c: Likewise.

From-SVN: r269703