arm: Fix multilib mapping for CDE extensions [PR100856].

arm: Fix multilib mapping for CDE extensions [PR100856].

On passing +cdecp[0-7] extension to the -march string in command line options,
multilib linking is failing as mentioned in PR100856. This patch fixes this issue by
generating a separate canonical string by removing compiler options which are not
required for multilib linking from march string and assign the new string to mlibarch
option. This mlibarch string is used for multilib comparison.

gcc/ChangeLog:

2021-06-10  Srinath Parvathaneni  <srinath.parvathaneni@arm.com>

	PR target/100856
	* common/config/arm/arm-common.c (arm_canon_arch_option_1): New function
	derived from arm_canon_arch.
	(arm_canon_arch_option): Call it.
	(arm_canon_arch_multilib_option): New function.
	* config/arm/arm-cpus.in (IGNORE_FOR_MULTILIB): New fgroup.
	* config/arm/arm.h (arm_canon_arch_multilib_option): New prototype.
	(CANON_ARCH_MULTILIB_SPEC_FUNCTION): New macro.
	(MULTILIB_ARCH_CANONICAL_SPECS): New macro.
	(DRIVER_SELF_SPECS): Add MULTILIB_ARCH_CANONICAL_SPECS.
	* config/arm/arm.opt (mlibarch): New option.
	* config/arm/t-rmprofile (MULTILIB_MATCHES): For armv8*-m, replace use
	of march on RHS with mlibarch.

gcc/testsuite/ChangeLog:

2021-06-10  Srinath Parvathaneni  <srinath.parvathaneni@arm.com>

	PR target/100856
	* gcc.target/arm/acle/pr100856.c: New test.
	* gcc.target/arm/multilib.exp: Add tests for cde options.