Change objfile::has_partial_symbols to return bool

Change objfile::has_partial_symbols to return bool

This changes objfile::has_partial_symbols and
quick_symbol_functions::has_symbols to return bool.

gdb/ChangeLog
2021-03-20  Tom Tromey  <tom@tromey.com>

	* objfiles.h (struct objfile) <has_partial_symbols>: Return bool.
	* symfile.h (struct quick_symbol_functions) <has_symbols>: Return
	bool.
	* symfile-debug.c (debug_qf_has_symbols): Return bool.
	* psymtab.c (psym_has_symbols): Return bool.
	* objfiles.c (objfile::has_partial_symbols): Return bool.
	* dwarf2/read.c (dw2_has_symbols): Return bool.