RISC-V: Eliminate unused parameter warning.

RISC-V: Eliminate unused parameter warning.

The parameter orig_fndecl is not used, use anonymous parameters instead.

../.././gcc/gcc/config/riscv/riscv-c.cc: In function ‘bool riscv_check_builtin_call(location_t, vec<unsigned int>, tree, tree, unsigned int, tree_node**)’:
../.././gcc/gcc/config/riscv/riscv-c.cc:207:11: warning: unused parameter ‘orig_fndecl’ [-Wunused-parameter]
      tree orig_fndecl, unsigned int nargs, tree *args)
           ^~~~~~~~~~~

gcc/ChangeLog:

	* config/riscv/riscv-c.cc (riscv_check_builtin_call): Eliminate warning.