Remove "struct" from foreach statements

Remove "struct" from foreach statements

Some versions of gcc have a bug that causes

    for (struct mumble : something)

... to give a compiler error.  We routinely work around this bug in
gdb, but apparently had not done so in a while.  This patch fixes the
remaining known cases of this problem.

gdb/ChangeLog
2019-05-03  Sandra Loosemore  <sandra@codesourcery.com>
	    Tom Tromey  <tom@tromey.com>

	* dictionary.c (collate_pending_symbols_by_language): Remove
	"struct" from foreach.
	* symtab.c (lookup_global_symbol_from_objfile)
	(lookup_symbol_in_objfile_from_linkage_name): Remove "struct" from
	foreach.
	* ser-tcp.c (net_open): Remove "struct" from foreach.
	* objfiles.c (objfile_relocate, objfile_rebase)
	(objfile_has_symbols): Remove "struct" from foreach.
	* minsyms.c (lookup_minimal_symbol_by_pc_section): Remove "struct"
	from foreach.
	* dwarf2read.c (handle_struct_member_die): Remove "struct" from
	foreach.
	* darwin-nat.c (thread_info_from_private_thread_info): Remove
	"struct" from foreach.
	* ada-lang.c (create_excep_cond_exprs)
	(ada_exception_catchpoint_cond_string): Remove "struct" from
	foreach.