The AAPCS specifies that the tuple types such as svint32x2_t
should use their arm_sve.h names when mangled instead of their
builtin names.
This patch also renames the internal types for the tuples to
be prefixed with __clang_, so they are not misinterpreted as
specified internal types like the non-tuple types which *are* defined
in the AAPCS. Using a builtin type for the tuples is a purely
a choice of the Clang implementation.