rs6000: Main function with stubs for parsing and output

rs6000: Main function with stubs for parsing and output

2021-07-20  Bill Schmidt  <wschmidt@linux.ibm.com>

gcc/
	* config/rs6000/rs6000-gen-builtins.c (rbtree.h): New #include.
	(num_bifs): New variable.
	(num_ovld_stanzas): Likewise.
	(num_ovlds): Likewise.
	(parse_codes): New enum.
	(bif_rbt): New variable.
	(ovld_rbt): Likewise.
	(fntype_rbt): Likewise.
	(bifo_rbt): Likewise.
	(parse_bif): New stub function.
	(create_bif_order): Likewise.
	(parse_ovld): Likewise.
	(write_header_file): Likewise.
	(write_init_file): Likewise.
	(write_defines_file): Likewise.
	(delete_output_files): New function.
	(main): Likewise.