[RS6000] Weak functions may not be file local

[RS6000] Weak functions may not be file local

A weak symbol defined in the current object file may not turn out to
be the definition used at link time, if other copies of the symbol
exist.  This means they can't be considered file local.

	PR target/67417
	* config/rs6000/predicates.md (current_file_function_operand): Don't
	return true for weak symbols.
	* config/rs6000/rs6000.c (rs6000_function_ok_for_sibcall): Likewise.

From-SVN: r227386