Various fixes for problems discovered stress-testing GC.

Various fixes for problems discovered stress-testing GC.

	* config/i386/i386.c (pic_label_name): Change to char pointer.
	(global_offset_table): New variable.
	(load_pic_register): Fill global_offset_table if it hasn't
	already been done.  Allocate pic_label_name dynamically.
	* ggc.h (empty_string): New variable.
	* ggc-simple.c (empty_string): Likewise.
	(init_ggc): Allocate empty_string and add as root.
	* stmt.c (digit_strings): New variable.
	(init_stmt): Add last_block_end_note as root.  Allocate and
	initialize digit_strings.
	(expand_asm_operands): Use empty_string and digit_string instead
	of string constants.
	* profile.c (init_arc_profiler): Allocate with ggc_alloc_string
	instead of xmalloc.
	(output_func_start_profiler): Likewise.
	* c-typeck.c (digest_init): Check if init is error_mark_node.

From-SVN: r29575