RISC-V: autovec: Export policy functions to global scope

RISC-V: autovec: Export policy functions to global scope

gcc/
	* config/riscv/riscv-vector-builtins.cc (get_tail_policy_for_pred):
	Remove static declaration to to make externally visible.
	(get_mask_policy_for_pred): Ditto.
	* config/riscv/riscv-vector-builtins.h (get_tail_policy_for_pred):
	New external declaration.
	(get_mask_policy_for_pred): Ditto.