* Mark SVE ACLE types as substitution candidates.
* Change mangling of svbfloat16_t from __SVBFloat16_t to
__SVBfloat16_t.
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
This is an ABI break with the old behaviour available via
"-fclang-abi-compat=17".