RISC-V: Add support for TLS stack protector canary access

RISC-V: Add support for TLS stack protector canary access

gcc/
	* config/riscv/riscv-opts.h (stack_protector_guard): New enum.
	* config/riscv/riscv.c (riscv_option_override): Handle
	the new options.
	* config/riscv/riscv.md (stack_protect_set): New pattern to handle
	flexible stack protector guard settings.
	(stack_protect_set_<mode>): Ditto.
	(stack_protect_test): Ditto.
	(stack_protect_test_<mode>): Ditto.
	* config/riscv/riscv.opt (mstack-protector-guard=,
	mstack-protector-guard-reg=, mstack-protector-guard-offset=): New
	options.
	* doc/invoke.texi (Option Summary) [RISC-V Options]:
	Add -mstack-protector-guard=, -mstack-protector-guard-reg=, and
	-mstack-protector-guard-offset=.
	(RISC-V Options): Ditto.

Signed-off-by: cooper <cooper.qu@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>