Document the GDB 7.7.1 release in gdb/ChangeLog

gdb/ChangeLog:

	GDB 7.7.1 released.
Don't complain about the source language when we have pubnames/pubtypes info.

gold/
	* gdb-index.cc (Gdb_index_info_reader): Don't complain about language
	if we have pubnames/pubtypes.