Hi,

This patch adds the support for pacbti multlilib linking by making
"-mbranch-protection=none" as default multilib option for arm-none-eabi
target.

Eg 1.

If the passed command line flags are (without mbranch-protection):
a) -march=armv8.1-m.main+mve -mfloat-abi=hard -mfpu=auto

"-mbranch-protection=none" will be used in the multilib matching.

Eg 2.

If the passed command line flags are (with mbranch-protection):
a) -march=armv8.1-m.main+mve+pacbti -mfloat-abi=hard -mfpu=auto  -mbranch-protection=pac-ret

"-mbranch-protection=standard" will be used in the multilib matching.

Regression tested on arm-none-eabi and bootstrapped on arm-none-linux-gnueabihf.

Ok for master?

Regards,
Srinath.

gcc/ChangeLog:

2023-01-11  Srinath Parvathaneni  <srinath.parvathaneni@arm.com>

        * config.gcc ($tm_file): Update variable.
        * config/arm/arm-mlib.h: Create new header file.
        * config/arm/t-rmprofile (MULTI_ARCH_DIRS_RM): Rename mbranch-protection
        multilib arch directory.
        (MULTILIB_REUSE): Add multilib reuse rules.
        (MULTILIB_MATCHES): Add multilib match rules.

gcc/testsuite/ChangeLog:

2023-01-11  Srinath Parvathaneni  <srinath.parvathaneni@arm.com>

        * gcc.target/arm/multilib.exp (multilib_config "rmprofile"): Update
        tests.
        * gcc.target/arm/pac-12.c: New test.
        * gcc.target/arm/pac-13.c: Likewise.
        * gcc.target/arm/pac-14.c: Likewise.