[SPARC][IAS] Add v8plus feature bit (#101367)
Implement handling for `v8plus` feature bit to allow the user to switch
between V8 and V8+ mode with 32-bit code.
Currently this only sets the appropriate ELF machine type and flags;
codegen changes will be done in future patches.
This is done as a prerequisite for `-mv8plus` flag on clang (#98713).
