More C++ build fixing

More C++ build fixing

Fixes:

In file included from ../../../binutils-gdb/gdb/gdbserver/server.h:61:0,
                 from ../../../binutils-gdb/gdb/gdbserver/server.c:19:
../../../binutils-gdb/gdb/gdbserver/target.h:442:50: error: second operand to the conditional operator is of type 'void', but the third operand is neither a throw-expression nor of type 'void'
    (*the_target->handle_new_gdb_connection) () : 0)
                                                  ^

Reported by Yuanhui Zhang.

gdb/gdbserver/ChangeLog:
2015-05-15  Pedro Alves  <palves@redhat.com>

	* target.h (target_handle_new_gdb_connection): Rewrite using if
	wrapped in do/while.