Add RISC-V architecture support

Add RISC-V architecture support

The original port of strace was done by Palmer Dabbelt
(eecs.berkeley.edu), based on strace 4.9.

* configure.ac: Define RISCV for riscv*.
* clone.c [RISCV]: Define ARG_* macros as for OR1K.
* defs.h [RISCV] (SUPPORTED_PERSONALITIES): Define to 2.
[RISCV] (NEED_UID16_PARSERS): Define to 1.
* linux/riscv/arch_regs.c: New file.
* linux/riscv/errnoent1.h: Likewise.
* linux/riscv/get_error.c: Likewise.
* linux/riscv/get_scno.c: Likewise.
* linux/riscv/get_syscall_args.c: Likewise.
* linux/riscv/ioctls_arch0.h: Likewise.
* linux/riscv/ioctls_arch1.h: Likewise.
* linux/riscv/ioctls_inc0.h: Likewise.
* linux/riscv/ioctls_inc1.h: Likewise.
* linux/riscv/signalent1.h: Likewise.
* linux/riscv/stat32.h: Likewise.
* linux/riscv/syscallent.h: Likewise.
* linux/riscv/syscallent1.h: Likewise.
* Makefile.am (EXTRA_DIST): Add them.

Signed-off-by: Richard W.M. Jones <rjones@redhat.com>