This patch add the following new multilibs.

thumb/v8.1-m.main+pacbti/mbranch-protection/nofp
thumb/v8.1-m.main+pacbti+dp/mbranch-protection/soft
thumb/v8.1-m.main+pacbti+dp/mbranch-protection/hard
thumb/v8.1-m.main+pacbti+fp/mbranch-protection/soft
thumb/v8.1-m.main+pacbti+fp/mbranch-protection/hard
thumb/v8.1-m.main+pacbti+mve/mbranch-protection/hard

Triggering the following compiler flags:

-mthumb -march=armv8.1-m.main+pacbti -mbranch-protection=standard -mfloat-abi=soft
-mthumb -march=armv8.1-m.main+pacbti+fp -mbranch-protection=standard -mfloat-abi=softfp
-mthumb -march=armv8.1-m.main+pacbti+fp -mbranch-protection=standard -mfloat-abi=hard
-mthumb -march=armv8.1-m.main+pacbti+fp.dp -mbranch-protection=standard -mfloat-abi=softfp
-mthumb -march=armv8.1-m.main+pacbti+fp.dp -mbranch-protection=standard -mfloat-abi=hard
-mthumb -march=armv8.1-m.main+pacbti+mve -mbranch-protection=standard -mfloat-abi=hard

Approved here:
<https://gcc.gnu.org/pipermail/gcc-patches/2022-July/598657.html>

gcc/

	* config/arm/t-rmprofile: Add multilib rules for march +pacbti
          and mbranch-protection.

gcc/testsuite/

	* gcc.target/arm/multilib.exp: Add pacbti related entries.