riscv: define _Addr and __sysinfo as int for 32bit

riscv: build on 32-bit

RISC-V: Use pthread typedefs from x86_64 for now

They at least have the union definitions with correct sizes. Given that
we don't support TLS for RISC-V the sizes of these don't really matter
for now.

RISC-V: Revert pthread_impl definitions

RISC-V: Fix core type definitions and sizes

RISC-V port