Update test cases to use -mcpu=unset/-march=unset feature introduced in
r15-3606-g7d6c6a0d15c.

gcc/testsuite/ChangeLog:

	* gcc.target/arm/pac-1.c: Use effective-target
	arm_arch_v8_1m_main_pacbti.
	* gcc.target/arm/pac-2.c: Likewise.
	* gcc.target/arm/pac-3.c: Likewise.
	* gcc.target/arm/pac-4.c: Likewise.
	* gcc.target/arm/pac-5.c: Likewise.
	* gcc.target/arm/pac-7.c: Likewise.
	* gcc.target/arm/pac-8.c: Likewise.
	* gcc.target/arm/pac-9.c: Likewise.
	* gcc.target/arm/pac-10.c: Likewise.
	* gcc.target/arm/pac-11.c: Likewise.
	* gcc.target/arm/pac-12.c: Added option "-mcpu=unset".
	* gcc.target/arm/pac-13.c: Likewise.
	* gcc.target/arm/pac-14.c: Likewise.
	* lib/target-supports.exp
	(check_effective_target_arm_pacbti_hw): Likewise.
	* gcc.target/arm/pac-6.c: Use effective-target
	arm_arch_v8_1m_main.
	* gcc.target/arm/pac-15.c: Use effective-target
	arm_arch_v8_1m_main_pacbti and added option "-mcpu=unset".

Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
Co-authored-by: Yvan ROUX <yvan.roux@foss.st.com>