[RS6000] ABI_V4 init of toc section

[RS6000] ABI_V4 init of toc section

Since 4c4a180d lto has turned off flag_pic when linking a fixed
position executable.  So flag_pic is zero in rs6000_file_start.
However, when we get to actually emitting code, flag_pic may be on
again.  This results in undefined references to ".LCTOC1".

	PR target/68662
	* config/rs6000/rs6000.c (need_toc_init): New var, set it
	whenever toc_label_name used.
	(rs6000_file_start): Don't set up toc section here,
	(rs6000_output_function_epilogue): do so here instead,
	(rs6000_xcoff_file_start): and here.
	* config/rs6000/rs6000.md (load_toc_aix_si): Set need_toc_init.
	(load_toc_aix_di): Likewise.

From-SVN: r233061