Don't derive partial_symbol from general_symbol_info

Don't derive partial_symbol from general_symbol_info

This patch partly reverts commit 8a6d42345 ("Change representation of
psymbol to flush out accessors"); specifically, it changes
partial_symbol to no longer derive from general_symbol_info.

The basic problem here is that the bcache compares objects bitwise,
and this change made it less likely that the relevant fields in the
psymbol would be fully initialized.  This could be seen by running a
test under valgrind on the Fedora-i686 buildbot.

I considered a simpler patch, namely just zeroing the psymbol's
"value" field in add_psymbol_to_bcache.  However, it wasn't clear to
me that this memset could not then be optimized away by the compiler.

Regression tested by the buildbot.  I think this should go in 8.3 as
well.

gdb/ChangeLog
2019-05-04  Tom Tromey  <tom@tromey.com>

	* psymtab.c (psymbol_name_matches, match_partial_symbol)
	(lookup_partial_symbol, print_partial_symbols)
	(recursively_search_psymtabs, sort_pst_symbols, psymbol_hash)
	(psymbol_compare): Update.
	(add_psymbol_to_bcache): Clear the entire psymbol.
	(maintenance_check_psymtabs): Update.
	* psympriv.h (struct partial_symbol): Don't derive from
	general_symbol_info.
	<obj_section, unrelocated_address, address,
	set_unrelocated_address>: Update.
	<ginfo>: New member.
	* dwarf-index-write.c (write_psymbols, debug_names::insert)
	(debug_names::write_psymbols): Update.