Better fix for PR 20499, including preventing strlen from being called on an uninitia...

Better fix for PR 20499, including preventing strlen from being called on an uninitialised name field.

	PR gprof/20499
	* corefile.c (BUFSIZE): Define.
	(STR_BUFSIZE): Define.
	(read_function_mappings): Use BUFSIZE and STR)BUFSIZE.
	(num_of_syms_in): Move buf, address and name arrays out of
	function and declare as static BUFSIZE arrays.
	Use STR_BUFSIZE when scanning for name and address.
	(core_create_syms_from): Revert previous delta.  Instead
	short circuit the parsing of a symbol if all three fields
	could not be found.