gdb/

gdb/
	Code cleanup.
	* dwarf2read.c (fixup_go_packaging): Do not check symtab->FILENAME for
	NULL.
	* linespec.c (add_sal_to_sals): Likewise.
	* psympriv.h (allocate_psymtab): Add ATTRIBUTE_NONNULL.
	* stack.c (print_frame): Do not check symtab->FILENAME for NULL.
	* symfile.h (allocate_symtab): Add ATTRIBUTE_NONNULL.
	* symtab.h (struct symtab): Add comment it is never NULL for filename.
	* tracepoint.c (set_traceframe_context): Do not check symtab->FILENAME
	for NULL.
	* tui/tui-source.c (tui_set_source_content): Likewise.