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.