Fix out-of-bounds write in RTL function reader (PR bootstrap/79952)

Fix out-of-bounds write in RTL function reader (PR bootstrap/79952)

gcc/ChangeLog:
	PR bootstrap/79952
	* read-rtl-function.c (function_reader::read_rtx_operand): Update
	x with result of extra_parsing_for_operand_code_0.
	(function_reader::extra_parsing_for_operand_code_0): Convert
	return type from void to rtx, returning x.  When reading
	SYMBOL_REF with SYMBOL_FLAG_HAS_BLOCK_INFO, reallocate x to the
	larger size containing struct block_symbol.

From-SVN: r246044