arm: Add support for dwarf debug directives and pseudo hard-register for PAC feature.
This patch teaches the DWARF support in gcc about RA_AUTH_CODE pseudo hard-register and also
updates the ".save", ".cfi_register", ".cfi_offset", ".cfi_restore" directives accordingly.
This patch also adds support to emit ".pacspval" directive when "pac ip, lr, sp" instruction
in generated in the assembly.
RA_AUTH_CODE register number is 107 and it's dwarf register number is 143.
Applying this patch on top of PACBTI series posted here
https://gcc.gnu.org/pipermail/gcc-patches/2022-August/599658.html and when compiling the following
test.c with "-march=armv8.1-m.main+mve+pacbti -mbranch-protection=pac-ret -mthumb -mfloat-abi=hard
fasynchronous-unwind-tables -g -O0 -S" command line options, the assembly output after this patch
looks like below: